import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		char[] S = sc.next().toCharArray();
		char[] T = sc.next().toCharArray();
		sc.close();
		int i=0;
		int ans = 0;
		while(!Arrays.equals(S, T)){
			if(T[i]!=S[i]){
				S[i]=T[i];
				ans++;
			}
			i++;
		}
		System.out.println(ans);
	}
}

/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