menstrual cycle

hello girls so I'm trying to track ovulation and I need to know what my average menstrual cycle is . I have been keeping track of my period for 4 months I got it on July 2nd lasted 5 days than on August 2nd lasted 5 days than I got it on August 31 lasted 5 days, September 30 lasted 5 days and on October 31 lasted 5 days. 
I came up with 32, 30, 31, 32.
what should I put on my average menstrual cycle?