#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
    cin >> n;
    double a = (n - 2) * 180.0 / n;
    printf("%.1f",a);
	return 0;
} 
/**************************************************************
	Problem: 1317
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/