user: 请将这段汇编代码片段转换成等效的C代码：

```asm
<trees>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x78,%rsp
  mov    %edi,0x6c(%rsp)
  movq   $0x1,0x60(%rsp)
  cmp    $0x1,%edi
  jbe    L82
  mov    %edi,%eax
  movl   $0x0,0x5c(%rsp)
  movq   $0x0,0x60(%rsp)
  sub    $0x1,%eax
  mov    %eax,0x68(%rsp)
  movq   $0x1,0x48(%rsp)
L420:
  mov    0x68(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L480
  sub    $0x2,%eax
  movq   $0x0,0x50(%rsp)
  mov    %eax,0x44(%rsp)
  movl   $0x0,0x40(%rsp)
  movq   $0x1,0x38(%rsp)
L39:
  mov    0x44(%rsp),%edx
  lea    0x1(%rdx),%eax
  cmp    $0x1,%eax
  jbe    L401
  mov    %edx,0x18(%rsp)
  movq   $0x0,0x20(%rsp)
  movl   $0x0,0x10(%rsp)
  movq   $0x1,(%rsp)
L77:
  mov    0x18(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L500
  sub    $0x1,%eax
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  movq   $0x0,0x8(%rsp)
  mov    %eax,0x14(%rsp)
L251:
  mov    0x14(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L28
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L97:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L97
  imul   %r14,%rbp
L28:
  mov    0x8(%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,0x8(%rsp)
  cmp    %r15d,0x18(%rsp)
  je     L411
  cmp    $0x1,%r15d
  jbe    L487
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L413:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L413
L453:
  subl   $0x1,0x14(%rsp)
  mov    %r15d,%r12d
  jmp    L251
  nopw   0x0(%rax,%rax,1)
L411:
  mov    (%rsp),%rax
  imul   0x8(%rsp),%rax
  mov    %rax,(%rsp)
L500:
  mov    0x20(%rsp),%rax
  mov    (%rsp),%rsi
  lea    (%rax,%rsi,2),%rax
  mov    %rax,0x20(%rsp)
  mov    0x10(%rsp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,0x14(%rsp)
  cmp    %eax,0x44(%rsp)
  je     L265
  cmpl   $0x1,0x14(%rsp)
  jbe    L575
  mov    0x10(%rsp),%eax
  movq   $0x0,(%rsp)
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  mov    %eax,0x8(%rsp)
L917:
  mov    0x8(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L554
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L746:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L746
  imul   %r14,%rbp
L554:
  mov    (%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,(%rsp)
  cmp    %r12d,0x10(%rsp)
  je     L316
  cmp    $0x1,%r15d
  jbe    L520
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L851:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L851
  subl   $0x1,0x8(%rsp)
  mov    %r15d,%r12d
  jmp    L917
L575:
  movq   $0x1,(%rsp)
  nopw   0x0(%rax,%rax,1)
L316:
  mov    0x14(%rsp),%eax
  subl   $0x1,0x18(%rsp)
  mov    %eax,0x10(%rsp)
  jmp    L77
  nopw   0x0(%rax,%rax,1)
L265:
  mov    0x38(%rsp),%rax
  imul   0x20(%rsp),%rax
  mov    %rax,0x38(%rsp)
L401:
  mov    0x50(%rsp),%rax
  mov    0x38(%rsp),%rsi
  lea    (%rax,%rsi,2),%rax
  mov    %rax,0x50(%rsp)
  mov    0x40(%rsp),%eax
  add    $0x1,%eax
  mov    %eax,0x58(%rsp)
  cmp    0x68(%rsp),%eax
  je     L354
  cmpl   $0x1,0x58(%rsp)
  jbe    L613
  mov    0x40(%rsp),%eax
  movl   $0x0,0x30(%rsp)
  movq   $0x0,0x38(%rsp)
  mov    %eax,0x34(%rsp)
  movq   $0x1,0x18(%rsp)
L614:
  mov    0x34(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L884
  sub    $0x1,%eax
  movl   $0x0,0x10(%rsp)
  mov    %eax,0x14(%rsp)
  movq   $0x0,0x20(%rsp)
  movq   $0x1,(%rsp)
L629:
  mov    0x14(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L216
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  mov    %r15d,0x8(%rsp)
L636:
  mov    0x8(%rsp),%edi
  lea    0x1(%r12),%r13d
  sub    %r12d,%edi
  call   <trees>
  imul   %rbp,%rax
  lea    (%r14,%rax,2),%r14
  cmp    %r13d,0x14(%rsp)
  je     L385
  cmp    $0x1,%r13d
  jbe    L440
  xor    %ebp,%ebp
  xor    %r15d,%r15d
L683:
  mov    %r15d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r15d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r15d,%eax
  add    $0x1,%r15d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L683
L459:
  mov    %r13d,%r12d
  jmp    L636
  nopw   0x0(%rax,%rax,1)
L385:
  mov    (%rsp),%rax
  imul   %r14,%rax
  mov    %rax,(%rsp)
L216:
  mov    0x20(%rsp),%rax
  mov    (%rsp),%rdx
  lea    (%rax,%rdx,2),%rax
  mov    %rax,0x20(%rsp)
  mov    0x10(%rsp),%eax
  add    $0x1,%eax
  mov    %eax,0x28(%rsp)
  cmp    0x34(%rsp),%eax
  je     L361
  cmpl   $0x1,0x28(%rsp)
  jbe    L696
  mov    0x10(%rsp),%eax
  movq   $0x0,(%rsp)
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  mov    %eax,0x8(%rsp)
L537:
  mov    0x8(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L244
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L931:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L931
  imul   %r14,%rbp
L244:
  mov    (%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,(%rsp)
  cmp    %r12d,0x10(%rsp)
  je     L84
  cmp    $0x1,%r15d
  jbe    L697
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L263:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L263
  subl   $0x1,0x8(%rsp)
  mov    %r15d,%r12d
  jmp    L537
L696:
  movq   $0x1,(%rsp)
  nopl   0x0(%rax,%rax,1)
L84:
  mov    0x28(%rsp),%eax
  subl   $0x1,0x14(%rsp)
  mov    %eax,0x10(%rsp)
  jmp    L629
  nopw   0x0(%rax,%rax,1)
L361:
  mov    0x18(%rsp),%rax
  imul   0x20(%rsp),%rax
  mov    %rax,0x18(%rsp)
L884:
  mov    0x38(%rsp),%rax
  mov    0x18(%rsp),%rsi
  lea    (%rax,%rsi,2),%rax
  mov    %rax,0x38(%rsp)
  mov    0x30(%rsp),%eax
  lea    0x1(%rax),%edx
  mov    %edx,0x8(%rsp)
  cmp    %eax,0x40(%rsp)
  je     L176
  cmpl   $0x1,0x8(%rsp)
  jbe    L423
  mov    0x30(%rsp),%eax
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  movq   $0x0,0x18(%rsp)
  mov    %eax,(%rsp)
L768:
  mov    (%rsp),%eax
  cmp    $0x1,%eax
  jbe    L784
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L630:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L630
  imul   %r14,%rbp
L784:
  mov    0x18(%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,0x18(%rsp)
  cmp    0x30(%rsp),%r12d
  je     L714
  cmp    $0x1,%r15d
  jbe    L38
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L310:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L310
  subl   $0x1,(%rsp)
  mov    %r15d,%r12d
  jmp    L768
L423:
  movq   $0x1,0x18(%rsp)
  cs nopw 0x0(%rax,%rax,1)
L714:
  mov    0x8(%rsp),%eax
  subl   $0x1,0x34(%rsp)
  mov    %eax,0x30(%rsp)
  jmp    L614
  nopw   0x0(%rax,%rax,1)
L697:
  subl   $0x1,0x8(%rsp)
  mov    $0x1,%ebp
  mov    %r15d,%r12d
  jmp    L537
L613:
  movq   $0x1,0x38(%rsp)
L176:
  mov    0x58(%rsp),%eax
  subl   $0x1,0x44(%rsp)
  mov    %eax,0x40(%rsp)
  jmp    L39
L354:
  mov    0x48(%rsp),%rax
  imul   0x50(%rsp),%rax
  mov    %rax,0x48(%rsp)
L480:
  mov    0x60(%rsp),%rax
  mov    0x48(%rsp),%rsi
  lea    (%rax,%rsi,2),%rax
  mov    %rax,0x60(%rsp)
  mov    0x5c(%rsp),%eax
  add    $0x1,%eax
  mov    %eax,0x40(%rsp)
  cmp    %eax,0x6c(%rsp)
  je     L82
  cmpl   $0x1,0x40(%rsp)
  jbe    L763
  mov    0x5c(%rsp),%eax
  movl   $0x0,0x30(%rsp)
  movq   $0x0,0x48(%rsp)
  lea    -0x1(%rax),%esi
  mov    %eax,0x34(%rsp)
  mov    %esi,0x38(%rsp)
  movq   $0x1,0x20(%rsp)
L783:
  cmpl   $0x1,0x34(%rsp)
  jbe    L223
  mov    0x38(%rsp),%eax
  movl   $0x0,0x10(%rsp)
  movq   $0x0,0x28(%rsp)
  mov    %eax,0x18(%rsp)
  movq   $0x1,(%rsp)
L605:
  mov    0x18(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L424
  sub    $0x1,%eax
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  movq   $0x0,0x8(%rsp)
  mov    %eax,0x14(%rsp)
L755:
  mov    0x14(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L536
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L852:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L852
  imul   %r14,%rbp
L536:
  mov    0x8(%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,0x8(%rsp)
  cmp    0x18(%rsp),%r15d
  je     L700
  cmp    $0x1,%r15d
  jbe    L688
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L899:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L899
L94:
  subl   $0x1,0x14(%rsp)
  mov    %r15d,%r12d
  jmp    L755
  xchg   %ax,%ax
L700:
  mov    (%rsp),%rax
  imul   0x8(%rsp),%rax
  mov    %rax,(%rsp)
L424:
  mov    0x28(%rsp),%rax
  mov    (%rsp),%rdx
  lea    (%rax,%rdx,2),%rax
  mov    %rax,0x28(%rsp)
  mov    0x10(%rsp),%eax
  add    $0x1,%eax
  mov    %eax,0x14(%rsp)
  cmp    0x34(%rsp),%eax
  je     L712
  cmpl   $0x1,0x14(%rsp)
  jbe    L514
  mov    0x10(%rsp),%eax
  movq   $0x0,(%rsp)
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  mov    %eax,0x8(%rsp)
L161:
  mov    0x8(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L807
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L571:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L571
  imul   %r14,%rbp
L807:
  mov    (%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,(%rsp)
  cmp    %r12d,0x10(%rsp)
  je     L898
  cmp    $0x1,%r15d
  jbe    L611
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L705:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L705
  subl   $0x1,0x8(%rsp)
  mov    %r15d,%r12d
  jmp    L161
L514:
  movq   $0x1,(%rsp)
  nopw   0x0(%rax,%rax,1)
L898:
  mov    0x14(%rsp),%eax
  subl   $0x1,0x18(%rsp)
  mov    %eax,0x10(%rsp)
  jmp    L605
  nopw   0x0(%rax,%rax,1)
L712:
  mov    0x20(%rsp),%rax
  imul   0x28(%rsp),%rax
  mov    %rax,0x20(%rsp)
L223:
  mov    0x48(%rsp),%rax
  mov    0x20(%rsp),%rcx
  lea    (%rax,%rcx,2),%rax
  mov    %rax,0x48(%rsp)
  mov    0x30(%rsp),%eax
  lea    0x1(%rax),%esi
  mov    %esi,0x28(%rsp)
  cmp    %eax,0x5c(%rsp)
  je     L507
  cmpl   $0x1,0x28(%rsp)
  jbe    L100
  mov    0x30(%rsp),%eax
  movl   $0x0,0x10(%rsp)
  movq   $0x0,0x20(%rsp)
  mov    %eax,0x18(%rsp)
  movq   $0x1,(%rsp)
L99:
  mov    0x18(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L528
  sub    $0x1,%eax
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  movq   $0x0,0x8(%rsp)
  mov    %eax,0x14(%rsp)
L333:
  mov    0x14(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L436
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L229:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L229
  imul   %r14,%rbp
L436:
  mov    0x8(%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,0x8(%rsp)
  cmp    0x18(%rsp),%r15d
  je     L196
  cmp    $0x1,%r15d
  jbe    L93
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L174:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L174
L253:
  subl   $0x1,0x14(%rsp)
  mov    %r15d,%r12d
  jmp    L333
  nopl   (%rax)
L196:
  mov    (%rsp),%rax
  imul   0x8(%rsp),%rax
  mov    %rax,(%rsp)
L528:
  mov    0x20(%rsp),%rax
  mov    (%rsp),%rsi
  lea    (%rax,%rsi,2),%rax
  mov    %rax,0x20(%rsp)
  mov    0x10(%rsp),%eax
  lea    0x1(%rax),%esi
  mov    %esi,0x14(%rsp)
  cmp    0x30(%rsp),%eax
  je     L273
  cmpl   $0x1,0x14(%rsp)
  jbe    L397
  mov    0x10(%rsp),%eax
  movq   $0x0,(%rsp)
  xor    %r12d,%r12d
  mov    $0x1,%ebp
  mov    %eax,0x8(%rsp)
L788:
  mov    0x8(%rsp),%eax
  cmp    $0x1,%eax
  jbe    L767
  lea    -0x1(%rax),%r15d
  xor    %r14d,%r14d
  mov    %r15d,%r13d
L729:
  mov    %r15d,%edi
  sub    %r13d,%edi
  call   <trees>
  mov    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  lea    (%r14,%rbx,2),%r14
  sub    $0x1,%r13d
  jae    L729
  imul   %r14,%rbp
L767:
  mov    (%rsp),%rax
  lea    0x1(%r12),%r15d
  lea    (%rax,%rbp,2),%rax
  mov    %rax,(%rsp)
  cmp    %r12d,0x10(%rsp)
  je     L139
  cmp    $0x1,%r15d
  jbe    L825
  xor    %ebp,%ebp
  xor    %r13d,%r13d
L564:
  mov    %r13d,%edi
  call   <trees>
  mov    %r12d,%edi
  sub    %r13d,%edi
  mov    %rax,%rbx
  call   <trees>
  imul   %rax,%rbx
  mov    %r13d,%eax
  add    $0x1,%r13d
  lea    0x0(%rbp,%rbx,2),%rbp
  cmp    %r12d,%eax
  jne    L564
  subl   $0x1,0x8(%rsp)
  mov    %r15d,%r12d
  jmp    L788
L397:
  movq   $0x1,(%rsp)
  nopw   0x0(%rax,%rax,1)
L139:
  mov    0x14(%rsp),%eax
  subl   $0x1,0x18(%rsp)
  mov    %eax,0x10(%rsp)
  jmp    L99
L100:
  movq   $0x1,0x20(%rsp)
  nopl   0x0(%rax,%rax,1)
L273:
  mov    0x28(%rsp),%eax
  subl   $0x1,0x34(%rsp)
  subl   $0x1,0x38(%rsp)
  mov    %eax,0x30(%rsp)
  jmp    L783
L611:
  subl   $0x1,0x8(%rsp)
  mov    $0x1,%ebp
  mov    %r15d,%r12d
  jmp    L161
L825:
  subl   $0x1,0x8(%rsp)
  mov    $0x1,%ebp
  mov    %r15d,%r12d
  jmp    L788
L38:
  subl   $0x1,(%rsp)
  mov    $0x1,%ebp
  mov    %r15d,%r12d
  jmp    L768
L520:
  subl   $0x1,0x8(%rsp)
  mov    $0x1,%ebp
  mov    %r15d,%r12d
  jmp    L917
L763:
  movq   $0x1,0x48(%rsp)
L507:
  mov    0x40(%rsp),%eax
  subl   $0x1,0x68(%rsp)
  mov    %eax,0x5c(%rsp)
  jmp    L420
L82:
  mov    0x60(%rsp),%rax
  add    $0x78,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L688:
  mov    $0x1,%ebp
  jmp    L94
L440:
  mov    $0x1,%ebp
  jmp    L459
L487:
  mov    $0x1,%ebp
  jmp    L453
L93:
  mov    $0x1,%ebp
  jmp    L253
```

assistant: ```c
unsigned long long trees(unsigned n) {
  if (n <= 1) {
    return 1;
  }
  unsigned long long res = 0;
  unsigned i;
  for (i = 0; i < n; i++) {
    res += 2 * trees(i) * trees(n - i - 1);
  }
  return res;
}
```