#include <bits/stdc++.h>
using namespace std;
int main(){
    float n,a;
    cin>>n;
    a=(n-2)*180/n;
    printf("%.1f",a);
}
/**************************************************************
	Problem: 1317
	User: chenmingyu
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/