#include <cmath>
#include <iomanip>
#include <iostream>

int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);

  double a;
  std::cin >> a;

  double left = 0.;
  double right = a;
  double DELTA = 0.00000000000001;
  while (right - left > DELTA) {
    double mid = left + (right - left) / 2;
    if (mid * mid - mid + std::sqrt(mid) < a) {
      left = mid;
    } else {
      right = mid;
    }
  }

  std::cout << std::fixed << std::setprecision(6) << (right + left) / 2;

  return 0;
}