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package counting;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.Scanner;

/**
 *
 * @author Janette
 */
public class Counting {

    static BigInteger one = BigInteger.ONE;
    static BigInteger two = new BigInteger("2");
    static BigInteger five = new BigInteger("5");
    static BigInteger[] a = new BigInteger[1001];

    public static void main(String[] args) throws FileNotFoundException {
        Scanner in = new Scanner(new File("counting.in"));
        PrintWriter out = new PrintWriter(new File("counting.out"));
        int n;

        a[0] = one;
        a[1] = two;
        a[2] = five;
        calc();
        while (in.hasNextInt()) {
            n = in.nextInt();
            out.println(a[n]);
            //System.out.println(a[n - 1]);
        }
        out.close();
    }

    public static void calc() {
        for (int x = 3; x < a.length; x++) {
            a[x] = a[x - 1].multiply(two).add(a[x - 2].add(a[x - 3]));
        }
    }
}