String and subsequence

Your friend recently got two strings *A* and *B* as his New Year gift. He challenges you with a task and if you solve it, he’ll give you a treat at Taj Hotel. Let’s see whether you are able to solve his given task. He asks you to come up with a new string *C* **(can possibly be A also)** which is the concatenation of *A* with itself a multiple numbers of times, such that string *B* is then a s