import java.util.*;
import java.io.*;

class Main{
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String S = br.readLine();
        String T = br.readLine();
        int ans=0;

        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);

    }

} import java.util.*; util.* java import java.io.*; io.* java class Main{
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String S = br.readLine();
        String T = br.readLine();
        int ans=0;

        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);

    }

} Main public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String S = br.readLine();
        String T = br.readLine();
        int ans=0;

        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);

    } main {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String S = br.readLine();
        String T = br.readLine();
        int ans=0;

        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);

    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) String S = br.readLine(); S br.readLine() br.readLine br String T = br.readLine(); T br.readLine() br.readLine br int ans=0; ans 0 for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        } 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)) {
                ans++;
            }
        } {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        } if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            } S.charAt(i)!=T.charAt(i) S.charAt(i) S.charAt S i T.charAt(i) T.charAt T i {
                ans++;
            } ans++ ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;
import java.io.*;

class Main{
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        
        String S = br.readLine();
        String T = br.readLine();
        int ans=0;

        for (int i=0; i<S.length(); i++) {
            if (S.charAt(i)!=T.charAt(i)) {
                ans++;
            }
        }
        System.out.println(ans);

    }

}