def fn(n):
    if n <= 2:
        return 1
    res = [0 for i in range(n)]
    res[0], res[1] = 1, 1
    for i in range(2, n):
        res[i] = res[i-1] + res[i-2]
    return res[-1]


n = int(input())
result = fn(n)
print(result)