/in/foo.cc: In function 'int main()':
/in/foo.cc:9:7: warning: iteration 9996 invokes undefined behavior [-Waggressive-loop-optimizations]
   c[i]=(long long)i*(i-1)*(i-2)*(i-3)/24;
   ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/in/foo.cc:8:15: note: within this loop
  for(int i=4;i<=maxn;i++)
              ~^~~~~~