1+1-1+1-1+1-1+1-1+1-1+1-1+1-...

i't equal to:

1+(1-1)+(1-1)+(1-1)+(1-1)+(1-1)+(1-1)+(1-...

and equal to:

1+1+(-1+1)+(-1+1)+(-1+1)+(-1+1)+...

In the first one as (1-1)=0 then the all thing is equal to 1

But in the second one as (1-1)=0 then the all thing is equal to 2

How to explain this?