#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float d;
    cin>>n;
    d=(n-2)*180/n;
	printf("%.1f",d);
	return 0;
	

	
}
 
/**************************************************************
	Problem: 1317
	User: fuyijun
	Language: C++
	Result: Wrong Answer
****************************************************************/