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();
      
      if(s.equals(t)){
        System.out.print("0");
        return;
      }
        
      
      int result = 0;
      for(int i=0; i < s.length(); i++){
      	if(!s.substring(i,i+1).equals(t.substring(i, i+1))){
          result++;
        }
      }
        
      System.out.print(result);
    }
}

/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