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