First Unique Character (Data & Analytics)

Return the index of the first character in a lowercase string that appears exactly once in the whole string, using 1-based indexing; return −1 if there is none.

输入格式

The first line contains n, and the second line contains the string; 1≤n≤100000, lowercase English letters only.

输出格式

Output a single integer answer.

样例 1

输入：

10
statistics

输出：

3

样例 2

输入：

11
hackthegame

输出：

3

样例 3

输入：

4
aabb

输出：

-1

样例说明

The outputs of the three public examples are, in order: 3; 3; -1. These answers have been checked by independent enumeration or direct simulation.