# -*- coding: utf-8 -*-
#DP
def funcDP(now):
    if now == N:return 1
    if now > N:return 0
    if dp[now] != 0:return dp[now]
    
    for i in range(0,2):
        dp[now] =dp[now] + funcDP(now + 2-i)
    return dp[now]

N =int(input())

dp =[0] * (N)
ans = funcDP(0)

print(ans)