RRDtool Average for 1 Day

Beginner at this rrd stuff

Basically I want to get the average traffic usage from an RRD File for one day

I used

rrdtool fetch bytesRcvd.rrd AVERAGE -r 86400 -s 1187691600(When the file begins) -e 1187778000 (One day later)

However when I run this command it gives me values for every 300 seconds. How do I get it to give me a single value for the one day time frame