#include<fstream>
using namespace std;
ifstream f("fractii.in");
ofstream g("fractii.out");
int n,i,j,nr;
int numarare(int n)
{nr=n;
for(i=2;i<=n;i++)
	if(i%2==0)nnr+=n/2;
        else nr+=n-1;
if(n%2==1)nr+=n-2;
return nr;
}
int main()
{f>>n;
g<<numarare(n);
return 0;
}