import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    } main {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String S = scan.next(); S scan.next() scan.next scan String[] s = S.split(""); s S.split("") S.split S "" String T = scan.next(); T scan.next() scan.next scan String[] t = T.split(""); t T.split("") T.split T "" int count = 0; count 0 for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        } {
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        } if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            } !(s[i].equals(t[i])) (s[i].equals(t[i])) s[i].equals s[i] s i t[i] t i {
                s[i] = t[i];
                count++;
            } s[i] = t[i] s[i] s i t[i] t i 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) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        String S = scan.next();
        String[] s = S.split("");
        String T = scan.next();
        String[] t = T.split("");
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!(s[i].equals(t[i]))){
                s[i] = t[i];
                count++;
            }
        }
        System.out.println(count);
    }
}
