import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        String[] S = str.split("");
        String str2 = sc.nextLine();
        String[] T = str2.split("");
        int c = 0;
        for (int i = 0; i < S.length; i++) {
            if ( S[i].equals(T[i]) ) {
                c = c;
            } else {
                c = c+1;
            }
        }
        System.out.println(c);
    }
}
/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