import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	} main {
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int count = 0; count 0 String S = sc.next(); S sc.next() sc.next sc String T = sc.next(); T sc.next() sc.next sc String[] SS = S.split(""); SS S.split("") S.split S "" String[] TT = T.split(""); TT T.split("") T.split T "" for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        } int i = 0; int i = 0; i 0 i < SS.length i SS.length SS SS.length i++ i++ i {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        } {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        } if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          } !SS[i].equals(TT[i]) SS[i].equals(TT[i]) SS[i].equals SS[i] SS i TT[i] TT i {
            SS[i] = TT[i];
            count = count + 1;
          } SS[i] = TT[i] SS[i] SS i TT[i] TT i count = count + 1 count count + 1 count 1 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 sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	}
} Main
import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
        int count = 0;
		String S = sc.next();  
        String T = sc.next();  
        String[] SS = S.split("");
        String[] TT = T.split(""); 
        for (int i = 0; i < SS.length; i++) {
          if(!SS[i].equals(TT[i])){
            SS[i] = TT[i];
            count = count + 1;
          }
        }
        
		System.out.println(count);
	}
}