#include<bits/stdc++.h>
using namespace std;
int main() {
	float n,d;
	cin>>n;
	d=(n-2.0)*180/n;
	printf("%.1f",d);
    return 0;
}

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