Lemonade - Implementation

function lemonadeChange(bills)
 fives := 0
 tens := 0
 for each bill in bills
 if bill = 5 then
 fives := fives + 1
 else if bill = 10 then
 if fives = 0 then
 return false
 fives := fives - 1
 tens := tens + 1
 else
 if tens > 0 and fives > 0 then
 tens := tens - 1
 fives := fives - 1
 else if fives >= 3 then
 fives := fives - 3
 else
 return false
 return true

Time: $O(n)$. Space: $O(1)$.