/in/foo.cc: In function 'int main()':
/in/foo.cc:32:8: warning: iteration 9998 invokes undefined behavior [-Waggressive-loop-optimizations]
   f[i] = f[i - 1] + f[i - 2];
   ~~~~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:31:20: note: within this loop
  for (int i = 3; i <= 10001; i++) {
                  ~~^~~~~~~~