Variable composition

I need to call the value of a variable using 2 different variables.

For example in this pseudo code:

instanceNumber=3
instance1="server1"
instance2="server2"
instance3="server3"

count=1
while count >= instanceNumber:
    instanceServer = 'instance'   count
    execute and action with instance
    count  = 1

In the image below you can see the flow I'm trying to create.

I have tried to do

- instance${count}

- ${'instance'${count}}

variableComposition.png