#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    int n;
    cin >> n;
    double sum_angle = (n - 2) * 180;
    double each_angle = sum_angle / n;
    cout << fixed << setprecision(1) << each_angle << endl;
    return 0;
}    
/**************************************************************
	Problem: 1317
	User: fuyijun
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/