CF124A.The number of positions

Petr stands in line of n people, but he doesn't know exactly which position he occupies. He can say that there are no less than a people standing in front of him and no more than b people standing behind him. Find the number of different positions Petr can occupy.

彼得站在一排 $n$ 个人中，但他并不确切知道自己所处的位置。他只知道：站在他前面的人数不少于 $a$ 人，站在他后面的人数不多于 $b$ 人。求彼得可能占据的不同位置的数量。

The only line contains three integers n, a and b (0 ≤ a, b < n ≤ 100).

唯一一行包含三个整数 $n$、$a$ 和 $b$（$0 ≤ a, b < n ≤ 100$）。

Print the single number — the number of the sought positions.

输出单个数字——所求位置的数量。

The possible positions in the first sample are: 2 and 3 (if we number the positions starting with 1).

In the second sample they are 3, 4 and 5.

第一个样例中可能的位置是：2 和 3（位置编号从 1 开始）。

第二个样例中可能的位置是：3、4 和 5。