#include <bits/stdc++.h>
using namespace std;
const int N = 1e6;
int n, k, ans;
string s;
char check(char b, char c) {
  for (int i = 0; i < 26; i++) {
    if (b != i + 65 && i + 65 != c) return i + 65;
  }
}
int main() {
  scanf("%d%d", &n, &k);
  cin >> s;
  if (k > 2) {
    for (int i = 0; i < n - 1; i++) {
      if (s[i] == s[i + 1]) {
        if (i + 2 < n) {
          char x = check(s[i + 2], s[i + 1]);
          s[i + 1] = x;
        } else
          s[i + 1] = check('!', s[i + 1]);
        ans++;
      }
    }
    cout << ans << endl;
    cout << s << endl;
    return 0;
  } else {
    string t = s;
    int ans2 = 0;
    for (int i = 0; i < n; i++) {
      if (i % 2 == 0) {
        if (s[i] != 'A') {
          s[i] = 'A';
          ans++;
        }
      } else {
        if (s[i] != 'B') {
          s[i] = 'B';
          ans++;
        }
      }
    }
    for (int i = 0; i < n; i++) {
      if (i % 2 != 0) {
        if (t[i] != 'A') {
          t[i] = 'A';
          ans2++;
        }
      } else {
        if (t[i] != 'B') {
          t[i] = 'B';
          ans2++;
        }
      }
    }
    if (ans <= ans2) {
      cout << ans << endl;
      cout << s << endl;
    } else {
      cout << ans2 << endl;
      cout << t << endl;
    }
  }
  return 0;
}
