#include <bits/stdc++.h>
using namespace std;
int main()
{
int n;
cin>>n;
printf("%.1f",(n-2)*180.0/n);
 
	return 0;
}

/**************************************************************
	Problem: 1317
	User: wqc123
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/