Extract a number from a complicated string

[Horacius ReX]

Hi,

I have to read some data from a file, and on each block it always
appears the followng string; xyz.vs.1-81_1 . It appears a lot of time
with different numbers like;

xyz.vs.1-81_1
xyz.vs.1-1234_1
xyz.vs.1-56431_1

and so on

My problem is that I need to extract from this string the number. For
instance in xyz.vs.1-81_1 I have to extract the number 81, and in
xyz.vs.1-1234_1 I need to get the number 1234.

What is the easiest way of doing this ?

Thanks