#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float c;
	cin>>n;
	c=(n-2)*180.0/n;
	printf("%.1f",c); 
	return 0;
}
 
/**************************************************************
	Problem: 1317
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/