import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public 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 l = S.length();
		int cont = 0;
		for (int i = 0; i < l; i++) {
			char s = S.charAt(i);
			char t = T.charAt(i);
			if (s != t) {
				cont++;
			}
		}
		System.out.print(cont);
	}
}
/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