def dfs(N,n,dp):
	if dp[n] != -1:return dp[n]
	dp[n] = dfs(N,n - 1,dp) + dfs(N,n - 2,dp)
	return dp[n]
N = int(raw_input())
dp = [-1 for i in range(N + 1)]
dp[0] = 1
dp[1] = 1
print dfs(N,N,dp)