import sys 

input = sys.stdin.readline 


n = int(input())


dp = [n * n] * (n + 1)
dp[0] = 1


for i in range(1, n + 1):
    if i - 2 >= 0:
        dp[i] = dp[i - 1] + dp[i - 2]
    else:
        dp[i] = dp[i - 1]
        
print(dp[n])