题解 | 清楚姐姐买竹鼠

#include <bits/stdc++.h>
using namespace std;

int main() {
    long long a, b, x; //需要为long long型
    while (cin >> a >> b >> x) {
        long long min_amount = a * x; //全买a元的
        if ( x % 3 == 0)
            min_amount = min(min_amount, + x / 3 * b); //全买b元套餐的
        else
            min_amount = min(min_amount,
                             x / 3 * b + x % 3 * a);//买最多b元的，不足只数买a元的
        min_amount = min(min_amount, x / 3 * b + b);//b元的多买一套
        cout << min_amount;
    }
}