The Tribonacci sequence Tn is defined as follows:
T0 = 0, T1 = 1, T2 = 1, and T(n+3) = T(n) + T(n+1) + T(n+2) for n >= 0.
Given n, return the value of Tn.
Example 1
Inputn = 4
Output4
Explanation
T_3 = 0 + 1 + 1 = 2
T_4 = 1 + 1 + 2 = 4
Example 2
Inputn = 25
Output1389537
Constraints
0 <= n <= 37
The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.