import java.util.Scanner;
public final class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);
		String a = sc.next();
		String b = sc.next();
		int count=0;
		
		for(int i =0;i<a.length();i++) {
			if(!(a.charAt(i)==b.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