Is it possible to buy several subscriptions?

It's not forbidden, but it's never necessary for optimal solution.

Each subscription for k or more concerts, you not need more then one.

Just why?

4 1
1000 5
1000 5
1000 5
1000 5
2 10

You need to buy two identical subscriptions to get 3600.

Ignore my post above, I misunderstood the problem statement.

But still, even if you understand, i still don't. In case of
4 1
1000 5
1000 5
1000 5
1000 5
2 10
or even, if we're not allowed to use the same subscription twice,
4 2
1000 5
1000 5
1000 5
1000 5
2 10
2 10
, why can't we have 3600? That is, if i understood you correctly...