2839번: 설탕 배달

#include <stdio.h>

int main()

{

int N, copyN, five = 0, three;

scanf("%d", &N);

five = N / 5; // 2

while (five >= 0)

{

copyN = N - (five * 5); // 6

three = copyN / 3;

if (copyN % 3 == 0)

break;

--five;

}

(N != (five * 5 + three * 3)) ? printf("-1") : printf("%d", five + three);

}