#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 10;
const int maxm = 30;
int n, m, t[maxn];
long long dp[maxn][2][2][2];
char s[maxn];
long long DP(int x, int l1, int l2, int l3) {
  if (x > n) return l2 == n - 1;
  if (l1 < x - 3 || l2 < x - 2 || l3 < x - 2) return 0;
  long long &r = dp[x][l1 & 1][l2 & 1][l3 & 1];
  if (r != -1) return r;
  r = 0;
  for (int i = 1; i <= m; i++) {
    int nowl1 = (i == t[x - 1] ? l1 + 1 : l2);
    int nowl2 = (i == t[x] ? l2 + 1 : max(nowl1, l3));
    int nowl3 = (i == t[x + 1] ? l3 + 1 : nowl2);
    r += DP(x + 1, nowl1, nowl2, nowl3);
  }
  return r;
}
int main() {
  scanf("%d%d%s", &n, &m, s + 1);
  for (int i = 1; i <= n; i++) t[i] = s[i] - 'a' + 1;
  memset(dp, -1, sizeof(dp));
  printf("%I64d\n", DP(1, 0, 0, 0));
  return 0;
}
