Hi, I am trying to create a multiphe IF statement but it keeps returning a "0" value. Can anyone please advise? The IF statement is as follows:

=IF(C13="2015001","2014012",IF(C13="2015002","2015001",IF(C13="2015003","2015002",IF(C13="2015004","2015003",IF(C13="2015005","2015004",IF(C13="2015006","2015005",IF(C13="2015007","2015006",IF(C13="2015008","2015007",IF(C13="2015009","2015008",IF(C13="2015010","2015009",IF(C13="2015011","2015010",IF(C13="2015012","2015011",IF(C13="2016001","2015012",)))))))))))))