#include<bits/stdc++.h>
using namespace std;
int main(){
	double n,p;
	cin>>n;
	p=(n-2)*180/n;
	printf("%.1f",p);
} 
/**************************************************************
	Problem: 1317
	User: xiaojingxuan
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/