#include <bits/stdc++.h>
using namespace std;
const int N = 100500;
int n, m;
char s[N];
int dp[N];
void solve() {
  scanf("%d%d%s", &n, &m, s);
  long long ans = (m - 1) * n;
  for (int i = 0; i < n; i++) {
    if (i - 1 >= 0 && s[i] != s[i - 1]) ans += (m - 1) * i;
    if (i + 1 < n && s[i] != s[i + 1]) ans += (m - 1) * (n - 1 - i);
  }
  for (int i = 0; i < n; i++) {
    dp[i] = 1;
    if (i - 1 >= 0 && s[i - 1] != s[i]) dp[i] = 2;
    if (i - 2 >= 0 && s[i - 1] != s[i] && s[i - 2] == s[i])
      dp[i] = dp[i - 1] + 1;
    ans -= dp[i] - 1;
  }
  printf("%lld\n", ans);
}
int main() {
  solve();
  0;
  return 0;
}
