#include <bits/stdc++.h>
int n, m;
char s[100100];
int main() {
  scanf("%d%d", &n, &m);
  scanf("%s", s);
  int l = 1;
  for (int i = 1; i < n; i++)
    if (s[i] != s[i - 1]) l++;
  long long ans = 1LL * l * n * (m - 1);
  for (int i = 0, j; i < n - 1; i++)
    if (s[i] != s[i + 1]) {
      for (j = i + 2; j < n; j++)
        if (s[j] != s[j - 2]) break;
      ans -= 1LL * (j - i) * (j - i - 1) / 2;
      i = j - 2;
    }
  printf("%I64d\n", ans);
  return 0;
}
