题解 | 牛牛学数列6
牛牛学数列6
https://www.nowcoder.com/practice/b6321648517247b2ac2e2f80cbc63ae1
n=int(input())
A=0
i=4
A1=0
A2=1
A3=1
if n==1:
print (0)
elif n<=3:
print(1)
else:
while i<=n:
A=A1+2*A2+A3
A1=A2
A2=A3
A3=A
i=i+1
print(A)
