IF statement in Measures

Hi,

I have a table with the following columns: product line, end of month inventory count, and month number, and I also have a date column linked to this table. I have a measure like this:

StartingInventory = CALCULATE(SUMX(Table, Table[Inventory Count]), PREVIOUSMONTH('Date'[Date))

and I want the measure to take the current month inventory count if it is the first month of the year, so I am trying without success:

StartingInventory = IF([MonthNumber]  <> 1, CALCULATE(SUMX(Table, Table[Inventory Count]), PREVIOUSMONTH('Date'[Date)), SUMX(Table, Table[Inventory Count]))

When I try entering in this formula, the formula bar doesn't seem to pick up the MonthNumber column for me to use in the conditional statement. Am I doing something wrong here?