题解 | #合法IP#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.regex.*;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String str = br.readLine();
        String regStr = "((2[0-4]\\d|25[0-5]|1\\d{2}|[1-9]\\d|\\d)\\.){3}(2[0-4]\\d|25[0-5]|1\\d{2}|[1-9]\\d|\\d)";
        if(str.matches(regStr)){
            System.out.println("YES");
        }else{
            System.out.println("NO");
        }
    }
}