Problem Statement

You are given a string S of length N.
Among its subsequences, count the ones such that all characters are different, modulo 10^9+7. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings.
Here, a subsequence of a string is a concatenation of one or more characters from the string without changing the order.

Input

Input is given from Standard Input in the following format:
N
S

Output

Print the number of the subsequences such that all characters are different, modulo 10^9+7.

Constraints

• $1 \leq N \leq 100000$
• S consists of lowercase English letters.
• |S|=N

Sample Input 1

4
abcd

Sample Output 1

15

Since all characters in S itself are different, all its subsequences satisfy the condition.

Sample Input 2

3
baa

Sample Output 2

5

The answer is five: b, two occurrences of a, two occurrences of ba. Note that we do not count baa, since it contains two as.

Sample Input 3

5
abcab

Sample Output 3

17

见题面 Input 部分

见题面 Output 部分