N-th Tribonacci Number

Try to solve the N-th Tribonacci Number problem.

Statement

Given a number n, calculate the corresponding Tribonacci number. The Tribonacci sequence TnT_n is defined as:

T0=0, T1=1, T2=1T_0 = 0,\space T_1 = 1,\space T_2 = 1, and  Tn+3=Tn+Tn+1+Tn+2, \space T_{n+3} = T_n + T_{n+1} + T_{n+2},\space for n>=0n >= 0

The input number, n, is a non-negative integer.

Constraints:

  • 0≤0 \leq n ≤37\leq 37
  • The answer is guaranteed to fit within a 32-bit integer, i.e., answer ≤231−1\leq 2 ^{31} - 1

Examples

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