复杂度O（26**2*n）

import os
import sys
n, k = map(int, input().split())
str = input()
ls = 'abcdefghijklmnopqrstuvwxyz'
lsi = {s: i for i, s in enumerate(ls)}
c = [[0] * 26]
for i in range(n):
    c.append([c[-1][i] for i in range(26)])
    s = str[i]
    c[-1][lsi[s]] = c[-2][lsi[s]] + 1
r = 0
for i in range(n - k + 1):
    for j in range(i + k, i + k * 26 + 1, k):
        if j >= len(c):
            break
        f = 1
        for s in range(26):
            if c[j][s] - c[i][s] > k:
                f = -1
                break
            elif 0 < c[j][s] - c[i][s] < k:
                f = 0
                break
        if f == 1:
            r += 1
        elif f == -1:
            break
print(r)