#include <bits/stdc++.h>
using namespace std;
template <class T>
T sqr(T x) {
  return x * x;
}
const int maxn = 100100;
long long dp[maxn][30];
char str[maxn];
int a[maxn];
int nex[22], now[22];
int n, m;
int main() {
  scanf("%d%d", &n, &m);
  scanf("%s", str);
  for (int i = 0; i <= n - 1; i++) a[i + 1] = str[i] - 'a' + 1;
  for (int i = 1; i <= m; i++) {
    int state = 1;
    if (a[1] == i) state |= 2;
    if (a[1] == i || a[2] == i) state |= 4;
    dp[1][state]++;
  }
  for (int i = 2; i <= n; i++)
    for (int state = 0; state <= 7; state++) {
      now[0] = i - 3 + (((state)&1) > 0);
      now[1] = i - 2 + (((state)&2) > 0);
      now[2] = i - 2 + (((state)&4) > 0);
      for (int j = 1; j <= m; j++) {
        for (int l = 1; l <= 3; l++) {
          if (a[i - 2 + l] == j)
            nex[l] = now[l - 1] + 1;
          else
            nex[l] = max(nex[l - 1], now[l]);
        }
        if (nex[1] >= i - 2 && nex[2] >= i - 1 && nex[3] >= i - 1)
          dp[i][(nex[1] - i + 2) | ((nex[2] - i + 1) << 1) |
                ((nex[3] - i + 1) << 2)] += dp[i - 1][state];
      }
    }
  long long ans = dp[n][0] + dp[n][1] + dp[n][4] + dp[n][5];
  cout << ans << endl;
}
