#include <bits/stdc++.h>
using namespace std;
int main(){
	double n;
	cin>>n;
	n=(n-2)*180/n;
	printf("%.1f",n);
	return 0;
}

/**************************************************************
	Problem: 1317
	User: zhouhongyi
	Language: C++
	Result: Accepted
	Time:37 ms
	Memory:2072 kb
****************************************************************/