N = int(input())

dp_dict = {}


def solve(i):
    if i == 0:
        return 1
    elif i < 0:
        return 0

    if i in dp_dict:
        return dp_dict[i]
    else:
        res = solve(i-2)+solve(i-1)
        dp_dict[i] = res
        return solve(i-2)+solve(i-1)


print(solve(N))