Can you give an example for some algebra $\mathcal A$ over $\mathbb N$ a non-zero finite additive measure $\mu $ on this algebra, which has a countably additive extension to the $\sigma$-algebra generated by this algebra, moreover, when shifting any set $A ∈ \mathcal F$ by an integer $n$, for the so obtained set $A + n$ was fulfilled: $A + n ∈ A$, $\mu (A + n) = \mu $(A)?