
import java.util.*;
import java.math.*;
public class Main {
	public static void main(String[] args){
		
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		String T = sc.next();
		int A = 0;
		
		char[] s2 = S.toCharArray();
		char[] t2 = T.toCharArray();
		
		for (int i = 0 ; i < s2.length; i++)
		{
			if (s2[i]!=t2[i])
			{A++;}
			
		}
		
		
		System.out.println(A);
   
        }
		
	}
/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