题解 | 清楚姐姐买竹鼠

#include <iostream>
using namespace std;
#define ll long long
int main() {
   ll a,b,x;
   cin>>a>>b>>x;
   ll pay=0;
   if(3*a>=b&&a<=b){
   pay+=(x/3)*b;
   pay+=(x%3)*a;
   }
  else if (3*a>=b&&a>b){
      pay+=(x/3)*b;
      if(x%3!=0){
        pay+=b;
      }
   }
   else{
    pay+=x*a;
   }
   cout<<pay;
}
// 64 位输出请用 printf("%lld")