#include<stdio.h>
void main() 
{
	int n;
	double m;
	scanf("%d",&n);
    n=n*1.0;
	m=(n-2.0)*180/n;
	printf("%.1f",m);
}
/**************************************************************
	Problem: 1317
	User: admin
	Language: C
	Result: Accepted
	Time:16 ms
	Memory:1144 kb
****************************************************************/