Accent in greek keyboard

If somebody knows the solution to the following pls let us know. The problem
is with the greek language. Next to the letter L (in the right side of it)
there is the accent symbol of the greek language. You press it, the you
press a letter (for example á) and zou got Ü. The problem is that when i do
press it the result is ´´á instead of getting Ü. It is like pressing two
times the key intead of one.

Any help is more than welcome