#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	printf("%.1f",(n*1.0-2)*180/n);
	
}
/**************************************************************
	Problem: 1317
	User: baizhoudeyueguang
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/