Problem:
Score : 100 points

Problem Statement

You are given four digits N_1, N_2, N_3 and N_4. Determine if these can be arranged into the sequence of digits "1974".

Constraints

0 \leq N_1, N_2, N_3, N_4 \leq 9

N_1, N_2, N_3 and N_4 are integers.

Input

Input is given from Standard Input in the following format:

N_1 N_2 N_3 N_4

Output

If N_1, N_2, N_3 and N_4 can be arranged into the sequence of digits "1974", print YES; if they cannot, print NO.

Sample Input 1

1 7 9 4

Sample Output 1

YES

We can get 1974 by swapping N_2 and N_3.

Sample Input 2

1 9 7 4

Sample Output 2

YES

We already have 1974 before doing anything.

Sample Input 3

1 2 9 1

Sample Output 3

NO

Sample Input 4

4 9 0 8

Sample Output 4

NO

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Diagnostics;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        string[] n = Console.ReadLine().Split();
        bool[] flag = new bool[4];
        for (int i = 0; i < 4; i++)
        {
            if (n[i] == "1") flag[0] = true;
            else if (n[i] == "9") flag[1] = true;
            else if (n[i] == "7") flag[2] = true;
            else if (n[i] == "4") flag[3] = true;
        }
        for (int i = 0; i < 4; i++)
        {
            if (!flag[i])
            {
                Console.WriteLine("NO");
                return;
            }
        }
        Console.WriteLine("YES");
    }
}