# fib !!

def solve():
    N = int(input())

    dp = [0] * (N + 3)
    dp[0] = 1

    for i, dpi in enumerate(range(N)):
        dp[i + 1] += dp[i]
        dp[i + 2] += dp[i]

    print(dp[N])


if __name__ == '__main__':
    solve()