#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float h;
	cin>>n;
	h=(n-2)*180.0/n;
	printf("%.1f",h);
} 
/**************************************************************
	Problem: 1317
	User: huanghengyi
	Language: C
	Result: Compile Error
****************************************************************/