codeup 2641

# codeup 2641
# 숏다리의 계단 오르기 

N = int(input())

count = 0


def climb(remains, penalty):
    global count

    if remains == 0:
        # 결과값 반환
        count += 1
        return

    elif remains < 0:
        return
    else:
        if penalty <= 0:
            penalty = 0

        if penalty == 0:
            # 모든 칸만큼 올라갈 수 있음
            climb(remains - 1, penalty - 1)
            climb(remains - 2, penalty - 1)
            climb(remains - 3, 2)

        else:
            climb(remains - 1, penalty - 1)
            climb(remains - 2, penalty - 1)


climb(N, 0)
print(count)