#include <bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	float A=((n-2)*180.0)/n;
	printf ("%.1f",A);
	return 0;
	}
/**************************************************************
	Problem: 1317
	User: ljl2
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/