$N$ particles $A, B, C, D, E, \ldots \ldots$ are situated at the corners of $N$ sided regular polygon of side $L$. Each of the particles moves with constant speed $v \cdot A$ always has its velocity along $A B, B$ along $B C$ and $C$ along $C D$ and so on. $\Lambda$ t what time and where will the particles meet each other?