Baltic_ACM_ICPC_E

// Baltic ACM ICPC E
#include <iostream>
using namespace std;
int main()
{
    int t1,t2,t3,n, var, ats=0;
    cin >> t1 >> t2 >> t3 >> n;
    while(n>0)
    {
        if(n>=3)
        {
            n-=3;
            if(t1>=t2 && t1>=t3){var=(t1+t2)+t1;}
            else if(t2>=t3 && t2>=t1){var=(t1+t2)+t2;}
            else if(t3>=t2 && t3>=t1){var=(t1+t2)+t3;}
            ats+=var;
        }
        else
        {
            if(t1>=t2 && t1>=t3)
            {
                n-=1;
                ats+=t1;
            }
            else if(t2>=t1 && t2>=t3)
            {
                n-=1;
                ats+=t2;
            }
            else if(t3>=t1 && t3>=t1)
            {
                n-=1;
                ats+=t3;
            }
        }
    }
    cout << ats << endl;
    return 0;
}