백준 C# - 2839

 

 

 

using System;
using System.Text;
using System.Threading;

namespace baek2
{
    class Program
    {
        public static void Main()
        {
            int a = int.Parse(Console.ReadLine());
            int answer = 0;
            int b = a / 5;

            while(true)
            {
                if(b < 0)
                {
                    Console.WriteLine(-1);
                    return;
                }
                if((a - ( b * 5 ) )% 3 == 0)
                {
                    answer = (a - (5 * b) ) / 3;
                    break;
                }
                b--;
            }
            Console.Write(answer+b);
        }
    }
}