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);

    }

}
/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