#include<bits/stdc++.h>
using namespace std;

int main(){
	int n;
	float d;
	cin>>n;
	d=(n-2)*180.0/n;
	printf("%.1f",d);
	return 0;
}

/**************************************************************
	Problem: 1317
	User: linzihang
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/