/in/foo.cc: In function 'int main()':
/in/foo.cc:11:7: warning: iteration 996 invokes undefined behavior [-Waggressive-loop-optimizations]
   a[i]=a[i-1]+a[i-2]+a[i-3];
   ~~~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:9:15: note: within this loop
  for(int i=4;i<=A;i++)
               ^