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



/**************************************************************
	Problem: 1317
	User: 15159808820
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/