import java.util.*;
import java.lang.*;
class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
    String s=sc.next();
    String t=sc.next();
    int count=0;
    for(int i=0;i<s.length();i++)
    {
      char c1=s.charAt(i);
      char c2=t.charAt(i);
      if(c1!=c2)
        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