import java.util.*;

class Fibo {

    static final Scanner input = new Scanner(System.in);

    public static void main(String[] args) {
        int n;

        System.out.print("n? ");
        n = input.nextInt();
        if (n < 0) {
            System.err.println("Erreur: n doit être positif: " + n);
            System.exit(1);
        }

        long f_2;               // F(n-2)
        long f_1 = 1;           // F(n-1)
        long f = 0;             // F(n)
        for (int i = 1; i <= n; i++) {
            f_2 = f_1;
            f_1 = f;
            f = f_1 + f_2;
        }

        System.out.println("F(" + n + ") = " + f);
    }
}