Excel - 添加到目前为止的纯月

I have a column [A] with date values (MM-DD-yYYY). I want to have another column [B] with a month value that is equal to 11 months from [A]. By months, I mean a simple count of 11 months, not 30days*11 months. This results in a [B] value that is always a calendar month -1 from [A]. So if [A1] holds the value of "11-20-2015" I would like [B1] to hold a value of "October". If [A2] holds a value of "03-29-2014", I would like [B2] to hold a value of "February".I have a column [A] with date values (MM-DD-yYY