import java.util.*;
public class Main{
	public static void main(String args[]){

		Scanner ob = new Scanner(System.in);
		String S = ob.next();
		String T = ob.next();
		int C = 0;

		for (int i = 0; i < S.length(); i++) {
			
			if(S.charAt(i) != T.charAt(i) ){
				C++;
			}
		}
		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