N = int(input())
dp = [0] * (N + 1)
dp[0] = 1

for i in range(N + 1):
    if i + 1 < N + 1:
        dp[i + 1] += dp[i]

    if i + 2 < N + 1:
        dp[i + 2] += dp[i]

print(dp[-1])