 import java.util.*;
import java.lang.*;
import java.io.*;

public class Main{

  public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  }
static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	}


}

  import java.util.*; util.* java import java.lang.*; lang.* java import java.io.*; io.* java public class Main{

  public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  }
static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	}


} Main public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  } main {
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  } InputReader in = new InputReader(); in new InputReader() String a = in.next(); a in.next() in.next in String b = in.next(); b in.next() in.next in if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    } a.equals(b) a.equals a b {
      System.out.println(0);
    } System.out.println(0) System.out.println System.out System System.out 0 {
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    } char[] arr_a = a.toCharArray(); arr_a a.toCharArray() a.toCharArray a char[] arr_b = b.toCharArray(); arr_b b.toCharArray() b.toCharArray b int n = arr_a.length; n arr_a.length arr_a arr_a.length int ans= 0; ans 0 for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      } int i=0; int i=0; i 0 i<n i n i++ i++ i {
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      } {
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      } if(arr_a[i]!=arr_b[i]){
          ans++;
        } arr_a[i]!=arr_b[i] arr_a[i] arr_a i arr_b[i] arr_b i {
          ans++;
        } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	} InputReader public BufferedReader reader; reader public StringTokenizer st; st public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		} InputReader {
			reader = new BufferedReader(new InputStreamReader(System.in));
		} reader = new BufferedReader(new InputStreamReader(System.in)) reader new BufferedReader(new InputStreamReader(System.in)) public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		} next {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		} while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			} st == null || !st.hasMoreTokens() st == null st null !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st {
				st = new StringTokenizer(nextLine());
			} st = new StringTokenizer(nextLine()) st new StringTokenizer(nextLine()) return st.nextToken(); st.nextToken() st.nextToken st public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		} nextLine {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		} try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			} catch (IOException e) {
				e.printStackTrace();
			} IOException e {
				e.printStackTrace();
			} e.printStackTrace() e.printStackTrace e {
				return reader.readLine();
			} return reader.readLine(); reader.readLine() reader.readLine reader return null; null public int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public class Main{

  public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  }
static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	}


} public class Main{

  public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  }
static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	}


} Main
 import java.util.*;
import java.lang.*;
import java.io.*;

public class Main{

  public static void main(String[] args){
    InputReader in = new InputReader();
    String a = in.next();
    String b = in.next();
    if(a.equals(b)){
      System.out.println(0);
    }
    else{
      char[] arr_a = a.toCharArray();
      char[] arr_b = b.toCharArray();
      int n = arr_a.length;
      int ans= 0;
      for(int i=0;i<n;i++){
        if(arr_a[i]!=arr_b[i]){
          ans++;
        }
      }
      System.out.println(ans);
    }
    
    
  }
static class InputReader {
		public BufferedReader reader;
		public StringTokenizer st;
 
		public InputReader() {
			reader = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String next() {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(nextLine());
			}
			return st.nextToken();
		}
 
		public String nextLine() {
			try {
				return reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return null;
		}
 
		public int nextInt() {
			return Integer.parseInt(next());
		}
	}


}

 
