#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float h;
    cin>>n;
    h=(n-2)*180.0/n;
    printf("%.1f",h);
    
	return 0;
}
/**************************************************************
	Problem: 1317
	User: yangjunwen
	Language: C
	Result: Compile Error
****************************************************************/