Suppose we know the process A by which a string s has been coded to a string r.

Implement a function that will decode r to get back the original string s.

Explanation of the known process A:
data: a string s composed of lowercase letters from a to z and a positive integer num
we know there is a correspondence between abcde...uvwxyz and 0, 1, 2 ..., 23, 24, 25 : 0 <-> a, 1 <-> b ...
If c is a character of s whose corresponding number is x, apply to x the function f: x-> f(x) = num * x % 26, then find ch the corresponding character of f(x).
Accumulate all these ch in a string r.
concatenate num and r and return the result.

code("mer", 6015) -> "6015ekx"
m <-> 12, 12 * 6015 % 26 == 4, 4 <-> e
e <-> 4, 4 * 6015 % 26 == 10, 10 <-> k
r <-> 17, 17 * 6015 % 26 == 23, 23 <-> x
We get "ekx" so the answer is: "6015ekx"

Task
A string s has been coded to a string r by the above process (A). Write a function decode(r) to get back s whenever it is possible.

Indeed it can happen that the decoding is impossible when positive integer num has not been correctly chosen. In that case return "Impossible to decode".

Example:
decode("6015ekx") -> "mer"
decode("5057aan") -> "Impossible to decode"

Tests:
decode("1273409kuqhkoynvvknsdwljantzkpnmfgf")
decode("761328qockcouoqmoayqwmkkic")

Good luck!

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