Consider a petrol pump which has a single petrol dispensing unit. Customers arrive there in accordance with a Poisson process having rate λ = 1 minutes. An arriving customer enters the petrol pump only if there are two or less customers in the petrol pump, otherwise he/she leaves the petrol pump without taking the petrol (at any point of time a maximum of three customers are present in the petrol pump). Successive service times of the petrol dispensing unit are independent exponential random variables having mean \(\frac{1}{2}\) minutes. Let X denote the average number of customers in the petrol pump in the long run. Then E(X) is equal to