This chall is about File Descripter(A.K.A fd)Using IDA, you can see below code.```int __cdecl main(int argc, const char **argv, const char **envp){  char buf; // [rsp+0h] [rbp-40h]  int v5; // [rsp+38h] [rbp-8h]  int v6; // [rsp+3Ch] [rbp-4h]
  puts("enter a number");  fflush(_bss_start);  __isoc99_scanf("%d", &v5;;  v6 = open("flag", 0) + 1001;  read(v5 - 1085645, &buf, 0x17uLL);  puts(&buf;;  return 0;}```If the read function works correctly, we can get flag file.So, What we have to do is just calculate the v5 variable.