Problem:
Score : 200 points

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.

Constraints

1 \leq N \leq 100000

S consists of lowercase English letters.

|S|=N

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.

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

Solution in Fortran (gfortran v4.8.4) (judge verdict: Accepted)

integer N
character(100000) S
integer CNT(26)
integer tmp
integer(16) ans
read*,N
read*,S

!実に読みづらい名前になってしまった
!各文字がどこにいられるかの場所
CNT=1
do i=1,N
  tmp=ichar(S(i:i))-ichar("a")+1
  CNT(tmp)=Cnt(tmp)+1
end do
ans=1
do i=1,26
  ans=mod(ans*cnt(i),10**9+7)
end do
ans=ans-1
print"(i0)",ans
end