import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		// 文字列の入力
		String s1 = sc.next();
		String s2 = sc.next();
      int counter =  s1.length();
		for(int i = 0; i < s1.length() ; i++){
			if(s1.substring( i, i + 1).equals (s2.substring(i, i + 1))){
				counter -= 1;
			}	
		}
		// 出力
		System.out.println(counter);
	}
}
/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