英语翻译
Description«acmnew»isasystemwhichallowstocreateprogrammingtasksinasimpleandprofessionalway.Whenyouaddatesttotheproblem,thecorrespondingformasksyouforthetestindex.Asinmostcasesitisclearwhichindexthenexttestwillhave,thesystemsuggeststhedefaultvalueoftheindex.Itiscalculatedasthesmallestpositiveintegerwhichisnotusedasanindexforsomepreviouslyaddedtest.Youaretoimplementthisfeature.Createaprogramwhichdeterminesthedefaultindexofthenexttest,giventheindexesofthepreviouslyaddedtests.
Input
Thefirstlinecontainsoneintegern(1 ≤ n ≤ 100000)—theamountofpreviouslyaddedtests.Thesecondlinecontainsndistinctintegersa1, a2, ..., an(1 ≤ ai ≤ 100000)—indexesofthesetests.
Output
Outputtherequireddefaultvalueforthenexttestindex.
SampleInput
3172
SampleOutput
3HINT