import java.util.Scanner;

/**
 * atcoder2
 */
public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    }
    
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    }
    
} Main public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    } main {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) String S = sc.nextLine(); S sc.nextLine() sc.nextLine sc String T = sc.nextLine(); T sc.nextLine() sc.nextLine sc int count = 0; count 0 for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        } {
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        } if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++; !((S.charAt(i)+"").equals(T.charAt(i)+"")) ((S.charAt(i)+"").equals(T.charAt(i)+"")) (S.charAt(i)+"").equals (S.charAt(i)+"") S.charAt(i) S.charAt S i "" T.charAt(i)+"" T.charAt(i) T.charAt 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) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    }
    
} public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    }
    
} Main
import java.util.Scanner;

/**
 * atcoder2
 */
public class Main {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine();
        String T = sc.nextLine();
        int count = 0;
        for(int i = 0; i < S.length(); i++){
            if(!((S.charAt(i)+"").equals(T.charAt(i)+"")))
            count++;
        }
        System.out.println(count);
    }
    
}