Number of solutions: 1

Solution 1:
ab@bb@bbbccc@c
@bbddbb@b@cccc
aa@d@bbbbde@cc
@adddd@d@dgecc
aaa@fddddd@e@c
a@hff@f@gggeee
ihh@hfjjj@g@ee
i@hih@kjjeeee@
iii@hkkj@j@len
@iiiik@jjjll@n
mm@m@kkkkj@lnn
mmmmmk@k@jjjn@
m@mm@mkkknj@nn
mmmmmmm@k@nnn@