#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    float j;
    cin>>n;
    j=(n-2)*180;
    j=j/n;
    printf("%.1f",j);
	return 0;
}

/**************************************************************
	Problem: 1317
	User: LYY001
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/