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();
    
    int ans = 0;
    
    for(int i = 0;i < S.length(); i++){        
        if(S.charAt(i)==T.charAt(i)){
            
        }else{
            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