import java.util.Scanner;

public class Main{
	public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      
      String s = sc.next();
      String t = sc.next();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    }
} import java.util.Scanner; Scanner 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();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    }
} Main public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      
      String s = sc.next();
      String t = sc.next();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    } main {
      Scanner sc = new Scanner(System.in);
      
      String s = sc.next();
      String t = sc.next();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    } 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 if(s.equals(t)){
        System.out.print("0");
        return;
      } s.equals(t) s.equals s t {
        System.out.print("0");
        return;
      } System.out.print("0") System.out.print System.out System System.out "0" return; int result = 0; result 0 for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      } int i=0; int i=0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      } {
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      } if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        } !s.substring(i,i+1).equals(t.substring(i, i+1)) s.substring(i,i+1).equals(t.substring(i, i+1)) s.substring(i,i+1).equals s.substring(i,i+1) s.substring s i i+1 i 1 t.substring(i, i+1) t.substring t i i+1 i 1 {
          result++;
        } result++ result System.out.print(result) System.out.print System.out System System.out result 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();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    }
} public class Main{
	public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      
      String s = sc.next();
      String t = sc.next();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    }
} Main
import java.util.Scanner;

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