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

public class Main {

    static Scanner sc = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
    static PrintWriter out = new PrintWriter(System.out);

    public static void main(String[] args) throws Exception {

        String str = sc.next();
        String t = sc.next();

        if(str.equals(t))
            out.println("0");
        else {

            List<Character> hash1 = new ArrayList<>();
            //Set<Character> hash2 = new HashSet<>();

            for(int i = 0;i < str.length(); ++i){

                if(str.charAt(i) != t.charAt(i))
                    hash1.add(str.charAt(i));

            }


            out.println(hash1.size());
        }

        out.flush();
        out.close();
        sc.close();
    }

    static final int MOD = (int) 1e9 + 7;
    static final double PI = 3.14159265358979323846;

    // takes array input
    public static int[] init(int n) {

        int[] arr = new int[n];

        for (int i = 0; i < n; ++i)
            arr[i] = sc.nextInt();

        return arr;
    }

    // finds GCD of two number
    public static int gcd(int a, int b) {

        if (a == 0) {
            return b;
        }

        return gcd(b % a, a);
    }

    // checks whether a number is prime or not
    public static boolean prime(int n) {

        if (n < 2)
            return false;

        for (int i = 2; i * i <= n; ++i)
            if (n % i == 0)
                return false;

        return true;
    }
}

/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz