Help me in using IF formula with condition

Hello,

plese help in my problem

in excell i have a column for revenues (say $50 M to $150 M)
my question is if the company revenue =50 and Revenue <70 it should print "SMALL" in next cell and if revenue >=70 and Revenue <100 it should print "MEDIUM" and revenue=100 and revenue <=150 should print "BIG".

what could be the formula for this?

please let me know on my email id basaarun@yahoo.com

Thanks,
Arun