백준 2839 - 설탕 배달

#include <iostream>
#include <stdio.h>
 
int main(void) {
    int weight;
    int ea3, ea5;
    
    ea3 = 0;
    ea5 = 0;
    
    scanf("%d", &weight);
    
    if(weight % 5 == 0){
        ea5 = weight/5;
        weight = 0;
    } else {
        ea5 = weight/5;
        while(true) {
            if((weight - ea5*5)%3 == 0) {
                ea3 = (weight - ea5*5)/3;
                break;
            } else {
                ea5 -= 1;
            }
            if(ea5 == -1) {
                ea3 = -1;
                break;
            }
        }
    }
    
    if(ea3 == -1)
        std::cout << "-1" << std::endl;
    else {
        std::cout << ea3+ea5 << std::endl;
    }
}