#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float i;
	cin>>n;
	i=(n-2)*180.0/n;
	printf("%.1f",i);
	
	
	
	
	
	
	return 0;
	
}
/**************************************************************
	Problem: 1317
	User: caiqiaoxi
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/