#include <iostream>
using namespace std;

int main()
{
    int cutletsOnSkillet, roastingTime, fullRoastingTime, cutletsCount;
    cin >> cutletsOnSkillet >> roastingTime >> cutletsCount;

    fullRoastingTime = roastingTime * 2;

    if( cutletsCount == cutletsOnSkillet)
    {
        cout <<  fullRoastingTime;
    }
    else if( cutletsCount < cutletsOnSkillet)
    {
        cout << cutletsCount * fullRoastingTime;
    }
    else if( cutletsCount > cutletsOnSkillet)
    {
        int cutletsDifference = cutletsCount - cutletsOnSkillet;

            if( cutletsDifference <= cutletsOnSkillet)
            {
                cout << (cutletsCount / cutletsOnSkillet) * fullRoastingTime + fullRoastingTime;
            }
            else if( cutletsDifference > cutletsOnSkillet)
            {
                cout <<  (cutletsCount / cutletsOnSkillet) * fullRoastingTime + (cutletsDifference/cutletsOnSkillet) * fullRoastingTime;
            }

    }
    return 0;

}