Mike And Bikes

Mike is a great rider. He has $N$ bikes. All of Mike's bikes initially have a certain levels of fuel $A_1, A_2, A_3, ..., A_N$. On some days Mike visits the fuel station and buys some $Y$ amount of fuel to fill in any one of his bikes. Now he wants to know, in how many ways can chose a bike and fill $Y$ amount of fuel in the chosen bike , so that its final amount of fuel would be $X$. Furthermor