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

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    }
} Main public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    } main {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) String a = scan.next(); a scan.next() scan.next scan String b = scan.next(); b scan.next() scan.next scan PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) Integer ll = a.length(); ll a.length() a.length a Integer ans = 0; ans 0 for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        } int i=0; int i=0; i 0 i<ll i ll i++ i++ i {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        } {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        } if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            } !a.substring(i,i+1).equals(b.substring(i,i+1)) a.substring(i,i+1).equals(b.substring(i,i+1)) a.substring(i,i+1).equals a.substring(i,i+1) a.substring a i i+1 i 1 b.substring(i,i+1) b.substring b i i+1 i 1 {
                ans++;
            } ans++ ans out.println(ans) out.println out ans out.close() out.close out String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    }
} Main
import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        String a = scan.next();
        String b = scan.next();
        PrintWriter out = new PrintWriter(System.out);
        
        Integer ll = a.length();
        Integer ans = 0;
        
        for (int i=0;i<ll;i++) {
            if (!a.substring(i,i+1).equals(b.substring(i,i+1))) {
                ans++;
            }
        }
        
        out.println(ans);
        out.close();
    }
}
