Microsoft Excel

Hello,
In column A I have specific numbers in each cell (i.e. A1= 1, A2=2, A3=3, A4=5), then in column B I have cells that have numbers as well (i.e. B1=1, B2=4, B3=18, B4=5). I want to count the number of cells that have matching numbers (i.e. A1 & B1 both have the number 1 in the cell, but A2 & B2 have different numbers. So for the above set the total number of matching cells is 2 (A1/B1 and A4/B4). How can I write a formula if I have hundreds of rows that I need to count the matches? Thank you so much in advance!