/in/foo.cc: In function 'int main()':
/in/foo.cc:17:18: warning: iteration 10000008 invokes undefined behavior [-Waggressive-loop-optimizations]
   sum[i]+=sum[i-1];//累加统计最终合格数量 
                  ^
/in/foo.cc:9:15: note: within this loop
  for(int i=2;i<=maxn;i++)
              ~^~~~~~