#### Sqrt Double

/**
* @file
* @brief Calculate the square root of any positive real number in \f$O(\log * N)\f$ time, with precision fixed using [bisection
* method](https://en.wikipedia.org/wiki/Bisection_method) of root-finding.
*
* @see Can be implemented using faster and better algorithms like
* newton_raphson_method.cpp and false_position.cpp
*/
#include <cassert>
#include <iostream>

/** Bisection method implemented for the function \f$x^2-a=0\f$
* whose roots are \f$\pm\sqrt{a}\f$ and only the positive root is returned.
*/
double Sqrt(double a) {
if (a > 0 && a < 1) {
return 1 / Sqrt(1 / a);
}
double l = 0, r = a;
/* Epsilon is the precision.
A great precision is
between 1e-7 and 1e-12.
double epsilon = 1e-12;
*/
double epsilon = 1e-12;
while (l <= r) {
double mid = (l + r) / 2;
if (mid * mid > a) {
r = mid;
} else {
if (a - mid * mid < epsilon) {
return mid;
}
l = mid;
}
}
return -1;
}

/** main function */
int main() {
double n{};
std::cin >> n;
assert(n >= 0);
// Change this line for a better precision
std::cout.precision(12);
std::cout << std::fixed << Sqrt(n);
}  