def lamp(n):
    dp = [0] * (n+1)
    dp[0] = 1
    dp[1] = 1
    # dp[2] = 2
 
    for i in range(2, n+1):
        dp[i] = dp[i-1] + dp[i-2]
    return dp[n]
n = int(input())
res = lamp(n)
print(res)