#参考——作者:未琢 https://www.bilibili.com/read/cv2017126 出处:bilibili
n, m = input().split(" ")
n = int(n)
m = int(m)
i = 3
fibo = [0, 1, 1] #加个0使得index与月份保持一致
s = 0
while i <= n:
if i <= m:
s = fibo[i-1] + fibo[i-2]
elif i == m+1:
s = fibo[i-1] + fibo[i-2] - 1
elif i > m+1:
s = fibo[i-1] + fibo[i-2] - fibo[i-m-1]
i += 1
fibo.append(s)
print(fibo[n])