#include<iostream>
#include<cmath>
using namespace std;
const long double EPS = 0.0000000001;
 
int main(){
  double a,b,x;
  cin >> a,b,x;
  double x_hight;
  x_hight= x / (a*a);
  double x_max;
  x_max= b-x_hight;
  double theta;
  double delta;
  int flag=1;
  theta = atan(a / x_max);
  cout << atan;
}