#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
long long dx[] = {-1, 0, 1, 0};
long long dy[] = {0, -1, 0, 1};
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  if (k == 2) {
    long long s1, s2;
    s1 = s2 = 0;
    for (long long i = 0; i < n; i++) {
      if (s[i] == 'A' && i % 2 == 1 || s[i] == 'B' && i % 2 == 0)
        s1++;
      else
        s2++;
    }
    cout << min(s1, s2) << "\n";
    for (long long i = 0; i < n; i++) {
      if (s1 < s2) {
        if (i % 2 == 0) {
          cout << 'A';
        } else
          cout << 'B';
      } else {
        if (i % 2 == 0) {
          cout << 'B';
        } else
          cout << 'A';
      }
    }
    return 0;
  }
  long long res = 0;
  for (long long i = 1; i < n; i++)
    if (s[i] == s[i - 1]) {
      res++;
      s[i] = '*';
    }
  for (long long i = 1; i < n - 1; i++)
    if (s[i] == '*') {
      if (s[i - 1] != 'A' && s[i + 1] != 'A')
        s[i] = 'A';
      else if (s[i - 1] != 'B' && s[i + 1] != 'B')
        s[i] = 'B';
      else
        s[i] = 'C';
    }
  if (s[n - 1] == '*' && s[n - 2] == 'A') s[n - 1] = 'B';
  if (s[n - 1] == '*') s[n - 1] = 'A';
  cout << res << "\n";
  cout << s << "\n";
}
