import java.util.*;

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

        Scanner sc = new Scanner(System.in);
        char[] a = sc.next().toCharArray();
        char[] b = sc.next().toCharArray();
        int n = a.length;
        int res = 0;
        for(int i=0; i<n; i++) {
            if(a[i] != b[i]) res++;
        }

        System.out.println(res);

    }

}
/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