A Look at an Octadecagon-3

In an 18 sided regular polygon with vertices labelled $A_1,A_2,\ldots,A_{18}$ in order,
the diagonals $A_1A_{13}$ and $A_6A_{15}$ intersect at a point $M$ ,
the diagonals $A_1A_{13}$ and $A_3A_{14}$ intersect at a point $N$ ,
the diagonals $A_3A_{14}$ and $A_6A_{15}$ intersect at a point $P$ .

Compute the angle $A_1PA_6.$