/in/foo.cc: In function 'int main()':
/in/foo.cc:14:7: warning: iteration 19999 invokes undefined behavior [-Waggressive-loop-optimizations]
   14 |   a[i]=a[i-1]+is99(i);
      |   ~~~~^~~~~~~~~~~~~~~
/in/foo.cc:13:15: note: within this loop
   13 |  for(int i=1;i<=20000;i++){
      |              ~^~~~~~~