#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,ni;
	float jiao;
	cin>>n;
	ni=(n-2)*180.0;
	jiao=ni/n;
	printf("%.1f",jiao);
}
/**************************************************************
	Problem: 1317
	User: wangyiyang
	Language: C++
	Result: Wrong Answer
****************************************************************/