#include <bits/stdc++.h>
using namespace std;
long long dp[100000 + 5][8];
char a[100000 + 5];
int main() {
  int n, m;
  scanf("%d%d%s", &n, &m, a + 1);
  for (int i = 1; i <= n; i++) a[i] -= 'a';
  for (int c = 0; c <= m - 1; c++)
    dp[1][1 | ((a[1] == c) << 1) | ((a[1] == c || a[2] == c) << 2)]++;
  for (int i = 1; i <= n - 1; i++)
    for (int c = 0; c <= m - 1; c++)
      for (int msk = 0; msk <= 7; msk++)
        if (dp[i][msk]) {
          int nmsk = 0;
          if (a[i] == c)
            nmsk |= msk & 1;
          else if (msk & 2)
            nmsk |= 1;
          if (a[i + 1] == c)
            nmsk |= msk & 2;
          else if ((msk & 4) == 0 && (nmsk & 1) == 0)
            continue;
          if (a[i + 2] == c)
            nmsk |= msk & 4;
          else if (nmsk & 2)
            nmsk |= 4;
          dp[i + 1][nmsk] += dp[i][msk];
        }
  long long ans = 0;
  for (int msk = 0; msk <= 7; msk++)
    if ((msk & 2) == 0) ans += dp[n][msk];
  printf("%lld\n", ans);
  return 0;
}
