Pepper and Iron Man

Pepper loves Iron Man very much. She does want Iron Man to go and fight with Thanos. So she gave a task to iron man. The task is as follows: 1. Iron man has been given two string $s1$, $s2$ and a string $p$ initially equal to $s2$. 2. He can concatenate string $s2$ to string $p$ any number of time. 3. He has to form string $p$, such that string $s1$ becomes the sub-sequence of $p$. Iron man is i