import java.util.Scanner;

public class Fibonacci {
	public static long fib_naive(int n) {
		if (n <= 1)
			return n;

		return fib_naive(n - 1) + fib_naive(n - 2);
	}

	public static long fib_optimized1(int n) {
		if (n <= 1)
			return (long) n;
		final long[] fibArray = new long[n+1];
		fibArray[0] = 0;
		fibArray[1] = 1;
		for (int i = 2; i < n+1; i++) {
			fibArray[i] = fibArray[i - 1] + fibArray[i - 2];
		}
		return fibArray[n];
	}

	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		int n = in.nextInt();

		System.out.println(fib_optimized1(n));
	}

}