import java.util.Scanner;
import java.util.Random;

public class MonteCarlo {
    private static Scanner input;
    static double montePI(int n)
    {
        int i,sum;
        double PI;
        double x, y;
        sum=0;
        
        Random r=new Random();
        for(i=1;i<n;i++)
        {
            x=r.nextDouble();
            y=r.nextDouble();
            if((x*x+y*y)<=1)
            {
                sum++;
            }
        }
        PI=4.0*sum/n;
        return PI;
    }
    public static void main(String[] args)
    {
        int n; 
        double PI;
        
        System.out.print("输入点的数量:");
        input = new Scanner(System.in);
        n=input.nextInt();
        PI=montePI(n);
        System.out.print("PI= "+PI);
    }
}