import java.util.*;
 
class Main {
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String S = sc.nextLine();
    String T = sc.nextLine();
    
    String[] Sar = S.split("");
    String[] Tar = T.split("");
    
    int c = 0;
    for(int i = 0; i < S.length(); i++){
      if(!Sar[i].equals(Tar[i])){
        c++;
      }
    }
    System.out.print(c);
  }
}
/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