import java.util.Scanner;
public class MonteCarlo {
    public static void main (String[] args) {
	double x, y;	   // (x,y) is point in plane
	double dist;	   // distance from (x,y) to (1/2,1/2)
	int numWithin = 0;	   // Number of points inside the circle
	System.out.println("How many trials?");
	Scanner getInput = new Scanner (System.in);
	int numTrials = getInput.nextInt();
	for (int trialNum=0; trialNum<numTrials; trialNum++) {
	    x = Math.random();
	    y = Math.random();
	    dist = Math.sqrt( (x-0.5)*(x-0.5) + (y-0.5)*(y-0.5) );
	    numWithin += (dist < 0.5) ? 1 : 0;
	}
	double fractionWithin = numWithin / (double) numTrials;
	System.out.printf("pi is approximately %f\n", 4*fractionWithin);
    }
}