Number of solutions: 1

Solution 1:
@bbbbbbbbccccc
abbddbbbb@cccc
aaaddb@bbdeecc
aadddddd@dgecc
aaa@fdddddgecc
ahhffff@gggeee
i@hhhfjjjggeee
ihhihfkjjeeee@
iiiihkkjjj@len
ii@iikkjjjllln
mmimmkkkkjll@n
mmmmm@kkjjjjnn
mmmmmmkkknj@nn
mmmm@mmkknnnnn