Recursive interleaving of strings X61846

The interleaving of two strings $x$ and $y$ is a string that contains all characters of $x$ and $y$ and preserves the relative order of the characters in both $x$ and $y$. For example, the interleaving of $abc$ and $xyz$ is $axbycz$. Write a program that prints the interleaving of every given pair of strings.

Define and use a recursive function

interleaving(x,y)

that returns the interleaving of two strings $x$ and $y$.

Input

The input consists of several pairs of strings.

Output

Print the interleaving of every given pair of strings.