#include <iostream>
#include <string>

using namespace std;

float Q_rsqrt( float number )
{
    long i;
    float x2, y;
    const float threehalfs = 1.5F;

    x2 = number * 0.5F;
    y = number;
    i = * ( long * ) &y;                        // evil floating point bit level hacking
    i = 0x5f3759df - ( i >> 1 );                // what the fuck
    y = * ( float * ) &i;                       
    y = y * ( threehalfs - ( x2 * y * y ) );    // 1st iteration
    y = y * ( threehalfs - ( x2 * y * y ) );    // 2nd iteration, can be removed

    return y;
}

int main()
{
    int number;
    cin >> number;
    cout << Q_rsqrt( number );
    return 0;
}