is a digit, that returns the xth character after c.

For every odd index i, you want to replace the digit s[i] with the result of the shift(s[i-1], s[i]) operation.

Return s __ after replacing all digits. It is guaranteed that shift(s[i-1], s[i]) will never exceed __'z'.

Note that shift(c, x) is not a preloaded function, but an operation to be implemented as part of the solution.

Input: s = "a1c1e1"