import java.util.*;
import java.io.*;
class Main{
  public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    String T = sc.next();
    int cnt = 0;
    char Sc[] = S.toCharArray();
    char Tc[] = T.toCharArray();
    for(int i = 0, len = S.length(); i < len; i++){
      if(Sc[i] != Tc[i]){
        cnt++;
      }
    }
    PrintWriter out = new PrintWriter(System.out);
    out.print(cnt);
    out.flush();
  }
}
/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