/in/foo.cc: In function 'int main()':
/in/foo.cc:12:8: warning: iteration 48 invokes undefined behavior [-Waggressive-loop-optimizations]
    a[i]=a[i-1]+a[i-2];
    ~~~~^~~~~~~~~~~~~~
/in/foo.cc:11:15: note: within this loop
  for(int i=3;i<=51;i++)
              ~^~~~