import java.util.*;

class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
		String str1  =  sc.next();
		String str2  =  sc.next();
      	int num = str1.length();
      
      	int cnt = 0;
      	char[] ary1 = new char[num];
      	char[] ary2 = new char[num];

      	for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        }
      	System.out.println(cnt);
    }
} import java.util.*; util.* java class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
		String str1  =  sc.next();
		String str2  =  sc.next();
      	int num = str1.length();
      
      	int cnt = 0;
      	char[] ary1 = new char[num];
      	char[] ary2 = new char[num];

      	for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        }
      	System.out.println(cnt);
    }
} Main public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
		String str1  =  sc.next();
		String str2  =  sc.next();
      	int num = str1.length();
      
      	int cnt = 0;
      	char[] ary1 = new char[num];
      	char[] ary2 = new char[num];

      	for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        }
      	System.out.println(cnt);
    } main {
    	Scanner sc = new Scanner(System.in);
		String str1  =  sc.next();
		String str2  =  sc.next();
      	int num = str1.length();
      
      	int cnt = 0;
      	char[] ary1 = new char[num];
      	char[] ary2 = new char[num];

      	for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        }
      	System.out.println(cnt);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String str1  =  sc.next(); str1 sc.next() sc.next sc String str2  =  sc.next(); str2 sc.next() sc.next sc int num = str1.length(); num str1.length() str1.length str1 int cnt = 0; cnt 0 char[] ary1 = new char[num]; ary1 new char[num] num char[] ary2 = new char[num]; ary2 new char[num] num for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        } int i = 0; int i = 0; i 0 i < str1.length() i str1.length() str1.length str1 i++ i++ i {
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        } {
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        } ary1[i] = str1.charAt(i) ary1[i] ary1 i str1.charAt(i) str1.charAt str1 i ary2[i] = str2.charAt(i) ary2[i] ary2 i str2.charAt(i) str2.charAt str2 i if(ary1[i] != ary2[i]){
            	cnt++;
            } ary1[i] != ary2[i] ary1[i] ary1 i ary2[i] ary2 i {
            	cnt++;
            } cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args
import java.util.*;

class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
		String str1  =  sc.next();
		String str2  =  sc.next();
      	int num = str1.length();
      
      	int cnt = 0;
      	char[] ary1 = new char[num];
      	char[] ary2 = new char[num];

      	for(int i = 0; i < str1.length() ; i++){
        	ary1[i] = str1.charAt(i);
        	ary2[i] = str2.charAt(i);

          	if(ary1[i] != ary2[i]){
            	cnt++;
            }
        }
      	System.out.println(cnt);
    }
}