

测试进位,对的。
99999999999999999999999999999999999999999999999999999999999 999999999
100000000000000000000000000000000000000000000000000999999998
100000000000000000000000000000000000000000000000000999999998
100000000000000000000000000000000000000000000000000999999998
1999999999
1999999999
2000000000