#include <bits/stdc++.h>
using namespace std;
int n;
double s;
double c;
int main(){
    cin>>n;
    s=(n-2)*180*1.0;
    c=s/n*1.0;
    printf("%.1f",c);
	return 0;
}
/**************************************************************
	Problem: 1317
	User: zengdongxin
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/