#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin>>n;
    float a;
    a=(n-2.0)*180.0/n;
    printf("%.1f",a);
    
}

/**************************************************************
	Problem: 1317
	User: huangluowei
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2072 kb
****************************************************************/