#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n=0;
	cin>>n;
	int njh=(n-2)*180;

	float ds=njh/(n * 1.0);
	printf("%.1f",ds);
	
	
	
	
	return 0;
}

/**************************************************************
	Problem: 1317
	User: 21A
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/