import java.util.*;
public class Main{
	public static void main(String[] args){
		Main obj=new Main();
		Scanner sc=new Scanner(System.in);
		String s=sc.next();
		String t=sc.next();
		int n=s.length(),count=0;

		for(int i=0;i<n;i++){
			if(s.charAt(i)!=t.charAt(i))
				count++;
		}

		System.out.println(count);
	}
}
/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