#include <iostream>
using namespace std;

int main() {
  double a, x;
  int k;

  cout << "Etner A: ";
  cin >> a;
  cout << "Enter K: ";
  cin >> k;
  if (k <= 0 && k % 2 != 0) {
    cout << "K must be positive and even";
    return 0;
  }
  cout << "Enter X: ";
  cin >> x;

  double summary = 1;
  for (int i = 2; i <= k; i += 2) {
    if (i == 2) {
      summary = (a - x / double(i)) * (a - x / double(i));
    } else {
      summary = (summary - x / double(i)) * (summary - x / double(i));
    }
  }
  summary *= 5.0;
  summary -= 3.0;
  cout << summary;
  return 0;
}