import java.util.*;
class Main{
	public static void main(String args[]){
		Scanner	sc = new Scanner(System.in);
		String s = sc.next();
		String t = sc.next();
		int c = 0;
		for(int i=0;i<s.length();i++){
			char ch1=s.charAt(i);
			char ch2=t.charAt(i);
			if(ch1!=ch2)
				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