count text in non consecutive cells in column
 

I have a spreadsheet with text entered in the columns. I want to count only
the information in non consecutive rows. Ex:
Row# Column#
1 N
5 B
8 G
10 N
15 B
18 C
20 I need a formula to total tne number of "N's" in this column "only" in
the rows shown and skiping the text in the other rows. (count row 1 but not
rows 3 and 4, count row 5 but not rows 6 and 7, etc.)