import java.util.Scanner;

//クラス名は必ずMainにする必要があります。



public class Main {
    public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	}
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	}
} Main public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	} main {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	} 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 char[] s_c = s.toCharArray(); s_c s.toCharArray() s.toCharArray s char[] t_c = t.toCharArray(); t_c t.toCharArray() t.toCharArray t int num = 0; num 0 for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        } int i = 0; int i = 0; i 0 i < s.length() i s.length() s.length s i++ i++ i {
            if(s_c[i] != t_c[i]){
                num++;
            }
        } {
            if(s_c[i] != t_c[i]){
                num++;
            }
        } if(s_c[i] != t_c[i]){
                num++;
            } s_c[i] != t_c[i] s_c[i] s_c i t_c[i] t_c i {
                num++;
            } num++ num System.out.println(num) System.out.println System.out System System.out num String args[] args public class Main {
    public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	}
} public class Main {
    public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	}
} Main
import java.util.Scanner;

//クラス名は必ずMainにする必要があります。



public class Main {
    public static void main(String args[] ) throws Exception {
		Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String t = sc.next();
        char[] s_c = s.toCharArray();
        char[] t_c = t.toCharArray();
        int num = 0;
        for(int i = 0; i < s.length(); i++){
            if(s_c[i] != t_c[i]){
                num++;
            }
        }
        System.out.println(num);
 	}
}