Take input of long ass string

while analyzing string
	find instance of "ATG" in string
		find instance of "TAG" in string
			are the number of characters between ATG and TAG divisible by 3?
				if yes break and print string from ATG to TAG
				if not continue
		find instance of "TGA" in string
			are the number of characters between ATG and TGA divisible by 3?
				if yes break and print string from ATG to TGA
				if not continue
		find instance of "TAA" in string
			are the number of characters between ATG and TAA divisible by 3?
				if yes break and print string from ATG to TAA
				if not continue
					if reached end of string break