Let m and n be two positive integers greater than 1 . If

[tex] \displaystyle\sf \lim_{a\to 0 }\bigg\lgroup \dfrac{e^{\cos(a^n)}-e}{a^m}\bigg\rgroup =-\bigg\lgroup \dfrac{e}{2}\bigg\rgroup [/tex]

Then the value of [tex]\dfrac{m}{n}[/tex] is ? ​