A sequence of numbers similar to the Fibonacci row

Michael is exploring a variation of Fibonacci numbers and has defined a sequence where the first sum is y = a + x. Subsequent sums follow the pattern of Fibonacci numbers: z = x + y, t = y + z, and so forth. The sequence continues for a total of $n$ terms. The sum of the pair of numbers in the last term of this sequence equals $b$. For example, if n = 4, the last term would be t + z = b. Given the values n, a, b, your task is to determine the value of $x$.