Problem 44254. Probability of red tulips (at both ends of a row)

I planted tulip bulbs in a row on my flower bed. I thought that I had planted white tulips all. However, later, it turned out that two RED tulip bulbs had been mixed in the planted bulbs!

Input (x): Number of all bulbs

Output (y): The probability that RED tulips will bloom at BOTH ENDs of the row.