n = int(input())
if n==1:
    print(0)
elif n==2 or n==3:
    print(1)
else:
    dp = [0]*(n+1)
    dp[1], dp[2], dp[3] = 0, 1, 1
    for i in range(4,n+1):
        dp[i] = dp[i-3]+2*dp[i-2]+dp[i-1]
    print(dp[-1])