题解 | 清楚姐姐买竹鼠

#include <iostream>
#include <algorithm>
#include <climits>
using namespace std;
using ll = long long;

int main() {
    ll a, b, x;
    cin >> a >> b >> x;
    
    ll cost1 = a * x;  // 全单买
    ll cost2 = ((x + 2) / 3) * b;  // 全3只一组买
    ll cost3 = (x / 3) * b + (x % 3) * a;  // 混合买（刚好满足）
  
    ll ans = min({cost1, cost2, cost3});
      
    cout << ans << endl;
    return 0;
}