General :: Maximum Date Value From A File?

I am facing a problem in finding out the maximum value of a field using awk .. The field is of date format i.e. (MM/DD/YYYY) ..

The contents of the file is :

2/2/2011 XYZ
2/2/2011 XYZ1
2/3/2011 ABC
2/4/2011 ABC

[Code]....

I need to find the maximum of the first column i.e. my output should be 2/12/2011 ..

I was using the below awk script : awk 'n < $0 {n=$0} {print n}{print $0}' <source_file having the above data>

But the output I am getting is 2/9/2011 instead of 2/12/2011 ...

what could be reason for this output and how can I get my desired result ..?