#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    float t;
    t=(n-2)*180.0/n;
printf("%.1f",t);
 
}
/**************************************************************
	Problem: 1317
	User: chenjiahui
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/