[BOJ] 2839 - 설탕배달

#include<iostream>

using namespace std;

int main(){
    int n;
    int result;
    cin >> n;
    int q5 = n / 5;

    while(true){
        if(q5 < 0){ 
            result = -1;
            break;
        }
        int r3 = (n - (5 * q5)) % 3;
        if(r3 == 0) {
            result = q5 + (n - (5 * q5)) / 3;
            break;
        } 
        q5--;
    }
    cout << result << "\n";
}