import java.util.Scanner;

//x0=2, x1=2,75, x2=4, P(3)=0,32954

public class Lagrange {

	public static int n;
	public static double fonk[];

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		System.out.println("Polinom derecesini giriniz:");
		n = sc.nextInt();

		fonk = new double[n + 1];

		for (int i = 0; i < n + 1; i++) {
			System.out.println("x " + n + "," + i + ":");
			fonk[i] = sc.nextDouble();
		}

		System.out.println("P(3) = " + P(3));

	}

	public static double P(double x) {

		double sonuc = 0;

		double l[] = new double[n + 1];

		for (int i = 0; i < n + 1; i++) {
			l[i] = 1;
		}

		for (int j = 0; j < n + 1; j++) {
			for (int i = 0; i < n + 1; i++) {
				if (i != j)
					l[j] *= (x - fonk[i]) / (fonk[j] - fonk[i]);
			}
		}

		for (int i = 0; i < n + 1; i++) {
			sonuc += l[i] * F(fonk[i]);
		}

		return sonuc;
	}

	public static double F(double x) {
		return 1 / x;
	}

}