import java.util.Scanner;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();

    char[] cS = S.toCharArray();
    char[] cT = T.toCharArray();

    int ans = 0;

    for(int i = 0; i < S.length(); i++) {
    	if(cS == cT) {
    		System.out.println(ans);
    		return;
    	}
      	if(cS[i] != cT[i]) {
    		ans++;
    	}
    }
    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