import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.StringTokenizer;

public class Main{

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        String a = fs.next();
        String b = fs.next();
        int ans = 0;
        for(int i = 0; i < a.length(); i++){
            if(a.charAt(i) != b.charAt(i)) ans++;
        }
        System.out.println(ans);
    }

    static void sort(int[] a){
        ArrayList<Integer>l = new ArrayList<>();
        for(int i: a)
            l.add(i);
        Collections.sort(l);
        for(int i = 0; i < a.length; i++)
            a[i] = l.get(i);
    }

    static class FastScanner{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer("");
        String next(){
            while(!st.hasMoreTokens())
                try{
                    st = new StringTokenizer(br.readLine());
                } catch(IOException e){
                    e.printStackTrace();
                }
            return st.nextToken();
        }

        int nextInt(){
            return Integer.parseInt(next());
        }
        int[] readArray(int n){
            int[] a = new int[n];
            for(int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }
        long nextLong(){
            return Long.parseLong(next());
        }
    }
}
/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