import java.io.BufferedReader;
import java.io.InputStreamReader;


class Main {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static String S, T;
    static int result = 0;

    public static void main(String[] args) throws Exception {
        S = br.readLine();
        T = br.readLine();
        
        for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        }
        System.out.println(result);
    }

} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io class Main {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static String S, T;
    static int result = 0;

    public static void main(String[] args) throws Exception {
        S = br.readLine();
        T = br.readLine();
        
        for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        }
        System.out.println(result);
    }

} Main static BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) static String S S T; T static int result = 0; result 0 public static void main(String[] args) throws Exception {
        S = br.readLine();
        T = br.readLine();
        
        for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        }
        System.out.println(result);
    } main {
        S = br.readLine();
        T = br.readLine();
        
        for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        }
        System.out.println(result);
    } S = br.readLine() S br.readLine() br.readLine br T = br.readLine() T br.readLine() br.readLine br for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        } int i = 0; int i = 0; i 0 i < S.length() i S.length() S.length S i++ i++ i {
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        } {
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        } if(S.charAt(i) != T.charAt(i)){
                result++;
           } S.charAt(i) != T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i {
                result++;
           } result++ result System.out.println(result) System.out.println System.out System System.out result String[] args args
import java.io.BufferedReader;
import java.io.InputStreamReader;


class Main {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static String S, T;
    static int result = 0;

    public static void main(String[] args) throws Exception {
        S = br.readLine();
        T = br.readLine();
        
        for(int i = 0; i < S.length(); i++){
           if(S.charAt(i) != T.charAt(i)){
                result++;
           }
        }
        System.out.println(result);
    }

}