#include<bits/stdc++.h>
using namespace std;
int main(){
	float n,j;
	cin>>n;
	j=(n-2)*180/n;
	printf("%.1f",j);
		
}
/**************************************************************
	Problem: 1317
	User: huangsiyuan
	Language: C++
	Result: Accepted
	Time:63 ms
	Memory:2072 kb
****************************************************************/