n = int(input())
a_list = [1, 1]
if n == 1 or n == 2:
    print(a_list[n - 1])
else:
    for i in range(3, n + 1):
        a_list.append(a_list[i - 2] + a_list[i - 3])
    print(a_list[n - 1])