import java.util.Scanner;
public class Main{

    public static void main(final String args[]) {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        String T = sc.next();
        int c = S.length();
        int cnt=0;
    for(int i=0; i<c; i++)
        if(S.charAt(i)!=T.charAt(i)){
            cnt++;
        }
    System.out.println(cnt);
    sc.close();

    }
}
/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