RUBY ; ATM ;EASY ; NZEC

I wrote the following code for the ATM project which is under the “Easy” tab:

c = gets.chomp.to_f
a = gets.chomp.to_f

if c<0 || c>2000 || c%5!=0 || a<=0 || a>2000 || c>a
puts a
else
puts a-c-0.50
end

It says Runtime error(NZEC)
Can someone tell me what is going on!?
Thank you
emorres25

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