import java.util.*;

class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String str01 = sc.next();
    String str02 = sc.next();
    
    int count = 0;
    if(str01.equals(str02)){
    	System.out.println(count);
    }else{
    	for(int i = 0; i < str01.length(); i++){
        	if(str01.charAt(i) != str02.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