import java.util.*;
import java.io.*;
public class Main{
	
	//make it false if Multiple test case is not in the question
	static boolean multipleTC = false;
	
	//for pre processing if needed
	void pre() throws Exception
	{}
		public static void main(String[] args) throws Exception{
			
		new Main().run();
	  }
	  



	// input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	}
	

	

	
	
	void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	}
	PrintWriter out;
		FastReader in;
		
			void p(Object o)
				{out.print(o);}
			void pln(Object o)
				{out.println(o);}
			void pnf(Object o)
				{out.println(o);
				out.flush();}
		
			String n()throws Exception
				{return in.next();}
		
			String nln()throws Exception
				{return in.nextLine();}
		
			int ni()throws Exception
				{return Integer.parseInt(in.next());}
		
			long nl()throws Exception
				{return Long.parseLong(in.next());}
		
			double nd()throws Exception
				{return Double.parseDouble(in.next());}
	
		class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		}
} import java.util.*; util.* java import java.io.*; io.* java public class Main{
	
	//make it false if Multiple test case is not in the question
	static boolean multipleTC = false;
	
	//for pre processing if needed
	void pre() throws Exception
	{}
		public static void main(String[] args) throws Exception{
			
		new Main().run();
	  }
	  



	// input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	}
	

	

	
	
	void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	}
	PrintWriter out;
		FastReader in;
		
			void p(Object o)
				{out.print(o);}
			void pln(Object o)
				{out.println(o);}
			void pnf(Object o)
				{out.println(o);
				out.flush();}
		
			String n()throws Exception
				{return in.next();}
		
			String nln()throws Exception
				{return in.nextLine();}
		
			int ni()throws Exception
				{return Integer.parseInt(in.next());}
		
			long nl()throws Exception
				{return Long.parseLong(in.next());}
		
			double nd()throws Exception
				{return Double.parseDouble(in.next());}
	
		class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		}
} Main //make it false if Multiple test case is not in the question
	static boolean multipleTC = false; multipleTC false PrintWriter out; out FastReader in; in //for pre processing if needed
	void pre() throws Exception
	{} pre {} public static void main(String[] args) throws Exception{
			
		new Main().run();
	  } main {
			
		new Main().run();
	  } new Main().run() new Main().run new Main() String[] args args // input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	} in_out {
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	} char[] s=n().toCharArray(); s n().toCharArray() n().toCharArray n() n char[] p=n().toCharArray(); p n().toCharArray() n().toCharArray n() n int count=0; count 0 for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  } int i=0; int i=0; i 0 i<s.length i s.length s s.length i++ i++ i {
			if(s[i]!=p[i])
			count++;
		  } {
			if(s[i]!=p[i])
			count++;
		  } if(s[i]!=p[i])
			count++; s[i]!=p[i] s[i] s i p[i] p i count++ count return ""+count; ""+count "" count int tc tc void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	} run {
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	} in = new FastReader() in new FastReader() out = new PrintWriter(System.out) out new PrintWriter(System.out) StringBuilder print=new StringBuilder(""); print new StringBuilder("") pre() pre int T = (multipleTC)?ni():1; T (multipleTC)?ni():1 (multipleTC) ni() ni 1 for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		} int t = 1; int t = 1; t 1 t<= T t T t++ t++ t {
		print.append(in_out(t)).append("\n");
		} {
		print.append(in_out(t)).append("\n");
		} print.append(in_out(t)).append("\n") print.append(in_out(t)).append print.append(in_out(t)) print.append print in_out(t) in_out t "\n" p(print) p print out.flush() out.flush out out.close() out.close out void p(Object o)
				{out.print(o);} p {out.print(o);} out.print(o) out.print out o Object o o void pln(Object o)
				{out.println(o);} pln {out.println(o);} out.println(o) out.println out o Object o o void pnf(Object o)
				{out.println(o);
				out.flush();} pnf {out.println(o);
				out.flush();} out.println(o) out.println out o out.flush() out.flush out Object o o String n()throws Exception
				{return in.next();} n {return in.next();} return in.next(); in.next() in.next in String nln()throws Exception
				{return in.nextLine();} nln {return in.nextLine();} return in.nextLine(); in.nextLine() in.nextLine in int ni()throws Exception
				{return Integer.parseInt(in.next());} ni {return Integer.parseInt(in.next());} return Integer.parseInt(in.next()); Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in long nl()throws Exception
				{return Long.parseLong(in.next());} nl {return Long.parseLong(in.next());} return Long.parseLong(in.next()); Long.parseLong(in.next()) Long.parseLong Long in.next() in.next in double nd()throws Exception
				{return Double.parseDouble(in.next());} nd {return Double.parseDouble(in.next());} return Double.parseDouble(in.next()); Double.parseDouble(in.next()) Double.parseDouble Double in.next() in.next in class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		} FastReader BufferedReader br; br StringTokenizer st; st public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			} FastReader {
				br = new BufferedReader(new InputStreamReader(System.in));
			} br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			} FastReader {
				br = new BufferedReader(new FileReader(s));
			} br = new BufferedReader(new FileReader(s)) br new BufferedReader(new FileReader(s)) String s s String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			} next {
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			} while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				} st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				} try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					} catch (IOException  e){
						throw new Exception(e.toString());
					} IOException  e {
						throw new Exception(e.toString());
					} throw new Exception(e.toString()); new Exception(e.toString()) {
						st = new StringTokenizer(br.readLine());
					} st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			} nextLine {
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			} String str = ""; str "" try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				} catch (IOException e){
					throw new Exception(e.toString());
				} IOException e {
					throw new Exception(e.toString());
				} throw new Exception(e.toString()); new Exception(e.toString()) {   
					str = br.readLine();
				} str = br.readLine() str br.readLine() br.readLine br return str; str public class Main{
	
	//make it false if Multiple test case is not in the question
	static boolean multipleTC = false;
	
	//for pre processing if needed
	void pre() throws Exception
	{}
		public static void main(String[] args) throws Exception{
			
		new Main().run();
	  }
	  



	// input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	}
	

	

	
	
	void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	}
	PrintWriter out;
		FastReader in;
		
			void p(Object o)
				{out.print(o);}
			void pln(Object o)
				{out.println(o);}
			void pnf(Object o)
				{out.println(o);
				out.flush();}
		
			String n()throws Exception
				{return in.next();}
		
			String nln()throws Exception
				{return in.nextLine();}
		
			int ni()throws Exception
				{return Integer.parseInt(in.next());}
		
			long nl()throws Exception
				{return Long.parseLong(in.next());}
		
			double nd()throws Exception
				{return Double.parseDouble(in.next());}
	
		class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		}
} public class Main{
	
	//make it false if Multiple test case is not in the question
	static boolean multipleTC = false;
	
	//for pre processing if needed
	void pre() throws Exception
	{}
		public static void main(String[] args) throws Exception{
			
		new Main().run();
	  }
	  



	// input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	}
	

	

	
	
	void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	}
	PrintWriter out;
		FastReader in;
		
			void p(Object o)
				{out.print(o);}
			void pln(Object o)
				{out.println(o);}
			void pnf(Object o)
				{out.println(o);
				out.flush();}
		
			String n()throws Exception
				{return in.next();}
		
			String nln()throws Exception
				{return in.nextLine();}
		
			int ni()throws Exception
				{return Integer.parseInt(in.next());}
		
			long nl()throws Exception
				{return Long.parseLong(in.next());}
		
			double nd()throws Exception
				{return Double.parseDouble(in.next());}
	
		class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		}
} Main
import java.util.*;
import java.io.*;
public class Main{
	
	//make it false if Multiple test case is not in the question
	static boolean multipleTC = false;
	
	//for pre processing if needed
	void pre() throws Exception
	{}
		public static void main(String[] args) throws Exception{
			
		new Main().run();
	  }
	  



	// input output handled here
	private String in_out(int tc) throws Exception{
		  //take input here
		  char[] s=n().toCharArray();
		  char[] p=n().toCharArray();

		//  int f1[]=new int[26];
		  //int f2[]=new int[26];
		  int count=0;
		  for(int i=0;i<s.length;i++){
			if(s[i]!=p[i])
			count++;
		  }

		return ""+count;

	}
	

	

	
	
	void run() throws Exception{
	//	long start_time=System.nanoTime();

	//	in = new FastReader("input.txt");  out = new PrintWriter("output.txt");
		in = new FastReader(); out = new PrintWriter(System.out);
		


		StringBuilder print=new StringBuilder("");
		pre();
		int T = (multipleTC)?ni():1;
		for(int t = 1; t<= T; t++){
		print.append(in_out(t)).append("\n");
		}

		p(print);
		//long end_time=System.nanoTime();
		//System.out.println("Running Time in nano sec : "+(end_time-start_time));
		
		out.flush();
		out.close();
	}
	PrintWriter out;
		FastReader in;
		
			void p(Object o)
				{out.print(o);}
			void pln(Object o)
				{out.println(o);}
			void pnf(Object o)
				{out.println(o);
				out.flush();}
		
			String n()throws Exception
				{return in.next();}
		
			String nln()throws Exception
				{return in.nextLine();}
		
			int ni()throws Exception
				{return Integer.parseInt(in.next());}
		
			long nl()throws Exception
				{return Long.parseLong(in.next());}
		
			double nd()throws Exception
				{return Double.parseDouble(in.next());}
	
		class FastReader{
			BufferedReader br;
			StringTokenizer st;
			
			public FastReader(){
				br = new BufferedReader(new InputStreamReader(System.in));
			}
	
			public FastReader(String s) throws Exception{
				br = new BufferedReader(new FileReader(s));
			}
	
			String next() throws Exception{
				while (st == null || !st.hasMoreElements()){
					try{
						st = new StringTokenizer(br.readLine());
					}catch (IOException  e){
						throw new Exception(e.toString());
					}
				}
				return st.nextToken();
			}
	
			String nextLine() throws Exception{
				String str = "";
				try{   
					str = br.readLine();
				}catch (IOException e){
					throw new Exception(e.toString());
				}  
				return str;
			}
		}
}