import java.util.*;
public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
} Main public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    } main {

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.next(); S sc.next() sc.next sc String T = sc.next(); T sc.next() sc.next sc int swap = 0; swap 0 int length = S.length(); length S.length() S.length S for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      } int i=0; int i=0; i 0 i<length i length i++ i++ i {
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      } {
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      } String s = S.substring(i,i+1); s S.substring(i,i+1) S.substring S i i+1 i 1 String t = T.substring(i,i+1); t T.substring(i,i+1) T.substring T i i+1 i 1 if(!s.equals(t)){
          swap++;
        } !s.equals(t) s.equals(t) s.equals s t {
          swap++;
        } swap++ swap System.out.println(swap) System.out.println System.out System System.out swap String[] args args public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
} public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
} Main
import java.util.*;
public class Main {
    public static void main(String[] args){

		Scanner sc = new Scanner(System.in);

		String S = sc.next();		
      String T = sc.next();
      int swap = 0;
      
      int length = S.length();
      for(int i=0;i<length;i++){
      	String s = S.substring(i,i+1);
        String t = T.substring(i,i+1);
        
        if(!s.equals(t)){
          swap++;
        }          
      }
	  System.out.println(swap);
		
		
    }
}