If a cell meets criteria, sum cells on that row

Hi. I have several spreadsheets where data is entered for various months. I need to total data for a certain month. I need to be able to say if A1 equals 1 (which represents January) then sum the data in row 1.

ex.
A B C
Month Money Source
1 1 50 C
2 10 200 P
3 3 10 C
4 1 20 C

How can I sum just the data from the rows that have Month=1?

Thank you in advance.