Ayush and Strings

While making the problems for Heritage Utsav, Trijeet came across an interesting string $S$ of length $N$. When Ayush saw the string he liked it very much. He liked it so much that now he wants a string $T$ such that $T$ contains the original string $K$ times as a substring. Also, he does not like long strings and would love it to be as small as possible. Trijeet does not know how to generate