/in/foo.cc: In function 'int main()':
/in/foo.cc:16:9: warning: iteration 10000007 invokes undefined behavior [-Waggressive-loop-optimizations]
   pre[i]=cnt;
   ~~~~~~^~~~
/in/foo.cc:15:15: note: within this loop
  for(int i=3;i<=10000010;i++){
              ~^~~~~~~~~~