/in/foo.cc: In function 'void factorial()':
/in/foo.cc:11:9: warning: iteration 999999 invokes undefined behavior [-Waggressive-loop-optimizations]
   mem[i]%=998244353;
   ~~~~~~^~~~~~~~~~~
/in/foo.cc:8:15: note: within this loop
  for(int i=1;i<=1000000;i++)
              ~^~~~~~~~~