#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
	cin>>n;	
	float d;
	d=(n-2) *180.0/n;
	printf("%.1f\n",d);	
}
/**************************************************************
	Problem: 1317
	User: fandaohan
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:2072 kb
****************************************************************/