#include<iostream>
using namespace std;

int main()
{
    int a,n,m,z;
    cin>>a>>n>>m>>z;
    int x=a,y=a;
    int sum=a;
    for(int i=3;i<=z;i++)
    {
        sum=sum+x;
        int t=y;
        y+=x;
        x=y;
    }
    cout<<sum;
}  ```