#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    float f=(n-2)*180.0;
    printf("%.1f",f/n);
	return 0;
}

/**************************************************************
	Problem: 1317
	User: ccf
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/