#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float a,i;
	cin>>n;
	a=(n-2)*180;
	i=a/n;
	printf("%",i);
	cout<<fixed<<setprecision(1)<<i;
} 
/**************************************************************
	Problem: 1317
	User: huxuanchen
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/