import java.util.*; 

class Main{
  public static void main(String args[]){
    Scanner scn = new Scanner(System.in);
    int count =0;
    String one =scn.next();
    String two =scn.next();
    for(int i=0;i<one.length();i++){
      if(one.charAt(i)!=two.charAt(i)){
        count++;
        continue;
      }
    }   
    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