#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float x;
	cin>>n;
	x=(n-2)*180.0/n;
	cout<<fixed<<setprecision(1)<<x;
	return 0;
}

/**************************************************************
	Problem: 1317
	User: linmiaoling
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/