[백준] 2839번 : 설탕 배달 - C#

https://www.acmicpc.net/problem/2839

using System;

class Program
{
    static void Main() {
        string s=Console.ReadLine();
        int n=int.Parse(s);
        int t=0;
        
        while(n%5!=0){
            n-=3;
            if(n<0){
                t=-1;
                break;
            }
            else t++;
        }
        if(n>0) t+=n/5;
        Console.Write(t);
    }
}