import cs1.Keyboard;

public class Montecarlo
{
	public static void main (String[] arg)
	{
		final double EPSILON = 1E-14;
		double x, y, r;
		int dentro = 0;
		
		
		System.out.print ("numero di lanci? ");
		int tiri = Keyboard.readInt();
		
		for (int i = 0; i < tiri; i++)
		{
			x = Math.random();
			y = Math.random();
			r = Math.pow (x, 2) + Math.pow (y, 2);
			if (r - 1.0 < EPSILON)
				dentro++;
		}
		
		System.out.println (4 * (double)dentro/tiri);
	}
}