import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;

public class Main {
	
	
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		String k = s.next();
		String m = s.next();
		
		int n = k.length(),ctr=0;
		for(int i=0;i<n;i++) {
			if(k.charAt(i)!=m.charAt(i)) {
				ctr++;
			}
		}
		System.out.println(ctr);
	}

}

/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