import java.io.*; 
import java.math.*;
import java.util.*;
import java.awt.Point;
 
public class Main {
	static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	//static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	}
	
	//Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
} Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		} @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          } compare {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          } if (arr2[0] < arr1[0])
					  return -1; arr2[0] < arr1[0] arr2[0] arr2 0 arr1[0] arr1 0 return -1; -1 1 if (arr2[0] > arr1[0])
					  return 1; arr2[0] > arr1[0] arr2[0] arr2 0 arr1[0] arr1 0 return 1; 1 return 0; 0 long[] arr1 arr1 long[] arr2 arr2 Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		} @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          } compare {
				  return arr1[2]-arr2[2]; //ascending order
	          } return arr1[2]-arr2[2]; //ascending order arr1[2]-arr2[2] arr1[2] arr1 2 arr2[2] arr2 2 int[] arr1 arr1 int[] arr2 arr2 import java.io.*; io.* java import java.math.*; math.* java import java.util.*; util.* java import java.awt.Point; Point java.awt public class Main {
	static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	//static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	}
	
	//Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
} Main static final long MOD = 998244353L; MOD 998244353L public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	} main {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	} FastScanner sc = new FastScanner(); sc new FastScanner() PrintWriter pw = new PrintWriter(System.out); pw new PrintWriter(System.out) int N = sc.ni(); N sc.ni() sc.ni sc int K = sc.ni()-1; K sc.ni()-1 sc.ni() sc.ni sc 1 String s = sc.next(); s sc.next() sc.next sc String str1 = s.substring(0,K); str1 s.substring(0,K) s.substring s 0 K String str = s.substring(K,K+1).toLowerCase(); str s.substring(K,K+1).toLowerCase() s.substring(K,K+1).toLowerCase s.substring(K,K+1) s.substring s K K+1 K 1 String str2 = s.substring(K+1); str2 s.substring(K+1) s.substring s K+1 K 1 pw.print(str1+str+str2) pw.print pw str1+str+str2 str1+str+str2 str1 str str2 pw.close() pw.close pw String[] args args //Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	} power { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	} long res = 1; res 1 x = x % p x x % p x p while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} y > 0 y 0 { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} if((y & 1)==1) 
				res = (res * x) % p; (y & 1)==1 (y & 1) y 1 1 res = (res * x) % p res (res * x) % p (res * x) res x p y = y >> 1 y y >> 1 y 1 x = (x * x) % p x (x * x) % p (x * x) x x p return res; res long x x long y y long p p public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	} sort {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	} Random rgen = new Random(); rgen new Random() for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} int i = 0; int i = 0; i 0 i < array.length i array.length array array.length i++ i++ i {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} int randomPosition = rgen.nextInt(array.length); randomPosition rgen.nextInt(array.length) rgen.nextInt rgen array.length array array.length int[] temp = array[i]; temp array[i] array i array[i] = array[randomPosition] array[i] array i array[randomPosition] array randomPosition array[randomPosition] = temp array[randomPosition] array randomPosition temp Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		}) Arrays.sort Arrays array new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		} return array; array int[][] array array public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	} sort {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	} Random rgen = new Random(); rgen new Random() for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} int i = 0; int i = 0; i 0 i < array.length i array.length array array.length i++ i++ i {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		} int randomPosition = rgen.nextInt(array.length); randomPosition rgen.nextInt(array.length) rgen.nextInt rgen array.length array array.length long[] temp = array[i]; temp array[i] array i array[i] = array[randomPosition] array[i] array i array[randomPosition] array randomPosition array[randomPosition] = temp array[randomPosition] array randomPosition temp Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		}) Arrays.sort Arrays array new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		} return array; array long[][] array array static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    } FastScanner BufferedReader br; br StringTokenizer st; st public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } FastScanner { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } next { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } IOException  e { 
                    e.printStackTrace(); 
                } e.printStackTrace() e.printStackTrace e { 
                    st = new StringTokenizer(br.readLine());
                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int ni() { 
            return Integer.parseInt(next()); 
        } ni { 
            return Integer.parseInt(next()); 
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nl() { 
            return Long.parseLong(next()); 
        } nl { 
            return Long.parseLong(next()); 
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nd() { 
            return Double.parseDouble(next()); 
        } nd { 
            return Double.parseDouble(next()); 
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        } nextLine { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        } String str = ""; str "" try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } IOException e {
                e.printStackTrace(); 
            } e.printStackTrace() e.printStackTrace e { 
                str = br.readLine(); 
            } str = br.readLine() str br.readLine() br.readLine br return str; str public class Main {
	static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	//static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	}
	
	//Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
} public class Main {
	static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	//static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	}
	
	//Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
} Main
import java.io.*; 
import java.math.*;
import java.util.*;
import java.awt.Point;
 
public class Main {
	static final long MOD = 998244353L;
	//static final long INF = -1000000000000000007L;
	//static final long MOD = 1000000007L;
	//static final int INF = 1000000007;
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		PrintWriter pw = new PrintWriter(System.out);
		int N = sc.ni();
		int K = sc.ni()-1;
		String s = sc.next();
		String str1 = s.substring(0,K);
		String str = s.substring(K,K+1).toLowerCase();
		String str2 = s.substring(K+1);
		pw.print(str1+str+str2);
		pw.close();
 	}
	
	//Fast exponentiation (x^y mod p)
	public static long power(long x, long y, long p) { 
		// Initialize result
		long res = 1;

		// Update x if it is more   
		// than or equal to p 
		x = x % p;  

		while (y > 0) { 
			// If y is odd, multiply x 
			// with result 
			if((y & 1)==1) 
				res = (res * x) % p; 

			// y must be even now 
			// y = y / 2 
			y = y >> 1;  
			x = (x * x) % p;  
		} 
		return res; 
	}
	
    public static int[][] sort(int[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    int[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<int[]>() {
			  @Override
        	  public int compare(int[] arr1, int[] arr2) {
				  return arr1[2]-arr2[2]; //ascending order
	          }
		});
		return array;
	}
    
    public static long[][] sort(long[][] array) {
    	//Sort an array (immune to quicksort TLE)
		Random rgen = new Random();
		for (int i = 0; i < array.length; i++) {
		    int randomPosition = rgen.nextInt(array.length);
		    long[] temp = array[i];
		    array[i] = array[randomPosition];
		    array[randomPosition] = temp;
		}
		Arrays.sort(array, new Comparator<long[]>() {
			  @Override
			  //Descending order
        	  public int compare(long[] arr1, long[] arr2) {
				  if (arr2[0] < arr1[0])
					  return -1;
				  if (arr2[0] > arr1[0])
					  return 1;
				  return 0;
	          }
		});
		return array;
	}
    
    static class FastScanner { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastScanner() { 
            br = new BufferedReader(new InputStreamReader(System.in)); 
        } 
  
        String next() { 
            while (st == null || !st.hasMoreElements()) { 
                try { 
                    st = new StringTokenizer(br.readLine());
                } catch (IOException  e) { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int ni() { 
            return Integer.parseInt(next()); 
        } 
  
        long nl() { 
            return Long.parseLong(next()); 
        } 
  
        double nd() { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() { 
            String str = ""; 
            try { 
                str = br.readLine(); 
            } catch (IOException e) {
                e.printStackTrace(); 
            } 
            return str;
        }
    }
}