import java.util.*;

class Main{
  public static void main(String args[]) {
    Scanner sc = new Scanner(System.in);
    String str_S = sc.next();
    char[] s = str_S.toCharArray();
    String str_T = sc.next();
    char[] t = str_T.toCharArray();
    int result = 0;
    for(int i = 0;i < s.length;i++) {
      if(s[i] != t[i]) {
        result++;
      }
    }
    System.out.println(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