Little Shino loves to play with coins. In the city she lives, there are $26$ different types of coins. Each coin is represented with a lowercase letter $a, b, c, ... , y, z$. Shino has some number of coins and she placed them in some random sequence, S, on the table. She is wondering how many pairs $(i, j)$ are there, where $i \le j$, such that number of distinct coins in sequence $S_i, S_{i+1}, S_{i+2}, ..., S_{j-1}, S_j$ is exactly equal to K. Two coins of same type (same letters) are considered equal and two coins of different types (different letters) are considered distinct.

Input:
First line contains one integer, K.
Second line contains a string, S, consist of lowercase letters only.

Output:
Print one integer, number of pairs $(i, j)$, where $i \le j$, such that number of distinct coins in sequence $S_i, S_{i+1}, S_{i+2}, ..., S_{j-1}, S_j$ is exactly equal to K.

Constraints:
$1 \le K \le 26$
$1 \le |S| \le 5*10^3$
S consists of lowercase letters only.