#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float h;
    cin>>n;
    h=(n-2)*180.0/n;
    printf("%.1f",h);
} 
/**************************************************************
	Problem: 1317
	User: huanghengyi
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/