#include<bits/stdc++.h>
using namespace std;
double a;
int main(){
	int n,m,k;
	cin>>n;
	
	a=((n-2)*180+0.0)/n;
	printf("%.1f\n",a); 
}
/**************************************************************
	Problem: 1317
	User: zhengzihao
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/