formula to show if amounts in 3 cells are equal to each other

I'm trying to make it obvious when a user filling a form has made an error, by returning a message in cell A5 if the amounts in cells A1, B1 and C1 are not all equal to each other.

I've tried:

=if(A1=B1=C1,"n/a","required")

=if((A1+B1+C1)/3=A1,"n/a","required")

neither of which worked.

I feel like this should be simple, but I can't get my Saturday brain around it. Any suggestions?

P.S. Is there a "not equal to" symbol available in excel formulas? 

Thanks in advance!