#include<iomanip>
using namespace std;
int main()
{
int n;
double r;
cin>>n;
r=(n‐2)*180*1.0/n;
cout<<fixed<<setprecision(1)<<r<<endl;
return 0;
}

/**************************************************************
	Problem: 1317
	User: HUANGYIBO
	Language: C++
	Result: Compile Error
****************************************************************/