import java.util.*;

class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String first = sc.next();
      	String last = sc.next();
      	
      	char[] fst = first.toCharArray();
      	char[] lst = last.toCharArray();
      	int count = 0;
      	for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        }
      System.out.println(count);
    }
} import java.util.*; util.* java class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String first = sc.next();
      	String last = sc.next();
      	
      	char[] fst = first.toCharArray();
      	char[] lst = last.toCharArray();
      	int count = 0;
      	for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        }
      System.out.println(count);
    }
} Main public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String first = sc.next();
      	String last = sc.next();
      	
      	char[] fst = first.toCharArray();
      	char[] lst = last.toCharArray();
      	int count = 0;
      	for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        }
      System.out.println(count);
    } main {
    	Scanner sc = new Scanner(System.in);
      	String first = sc.next();
      	String last = sc.next();
      	
      	char[] fst = first.toCharArray();
      	char[] lst = last.toCharArray();
      	int count = 0;
      	for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        }
      System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String first = sc.next(); first sc.next() sc.next sc String last = sc.next(); last sc.next() sc.next sc char[] fst = first.toCharArray(); fst first.toCharArray() first.toCharArray first char[] lst = last.toCharArray(); lst last.toCharArray() last.toCharArray last int count = 0; count 0 for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        } int i = 0; int i = 0; i 0 i < fst.length i fst.length fst fst.length i++ i++ i {
        	if(fst[i] != lst[i]){
            	count++;
            }
        } {
        	if(fst[i] != lst[i]){
            	count++;
            }
        } if(fst[i] != lst[i]){
            	count++;
            } fst[i] != lst[i] fst[i] fst i lst[i] lst i {
            	count++;
            } count++ count System.out.println(count) System.out.println System.out System System.out count String[] args args
import java.util.*;

class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	String first = sc.next();
      	String last = sc.next();
      	
      	char[] fst = first.toCharArray();
      	char[] lst = last.toCharArray();
      	int count = 0;
      	for(int i = 0; i < fst.length; i++){
        	if(fst[i] != lst[i]){
            	count++;
            }
        }
      System.out.println(count);
    }
}