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

}
/**************************************************************
	Problem: 1317
	User: zhuangsongyu
	Language: C++
	Result: Accepted
	Time:20 ms
	Memory:2072 kb
****************************************************************/