#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float a;
	scanf("%d",&n);
	a=(n-2)*180.0/n*1.0;
	printf("%.1f",a);
}
/**************************************************************
	Problem: 1317
	User: toughuatao1
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2076 kb
****************************************************************/