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

public class Main {
  public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  }
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
  public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  }
} Main public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  } main {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  } Scanner s = new Scanner(System.in); s new Scanner(System.in) String S = s.next(); S s.next() s.next s String T = s.next(); T s.next() s.next s int count = 0; count 0 for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	} int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
		if(S.charAt(i) != T.charAt(i)) count++;
	} {
		if(S.charAt(i) != T.charAt(i)) count++;
	} if(S.charAt(i) != T.charAt(i)) count++; S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args public class Main {
  public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  }
} public class Main {
  public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  }
} Main
import java.util.*;
import java.io.*;

public class Main {
  public static void main(String[] args) {
	Scanner s = new Scanner(System.in);
	String S = s.next();
	String T = s.next();
	int count = 0;
	for(int i = 0; i < S.length(); i++){
		if(S.charAt(i) != T.charAt(i)) count++;
	}
	System.out.println(count);
    
  }
}