I can't add

I keep a spreadsheet at work for all my mileage. I have it automatically add it all up and figure stuff out for me. Like how many miles for the month, year, how many left I have to run for the month/year to reach my goals etc. However, because I use this to really keep track of my running I sometimes forget how to add. Like today, I just opened my spreadsheet to log my weekend hours and I was 5 miles off. So if you notice an increase of 5 miles in my mileage tracker, that's what it is. I didn't get up and do a 5 mile run this morning or anything crazy like that, I just can't add.