#include <bits/stdc++.h>
using namespace std;
int a, b, c, d, ans, ans1, ans2;
string s;
int main() {
  cin >> a >> b;
  cin >> s;
  if (b != 2) {
    for (int i = 1; i <= a - 2; i++) {
      if (s[i] == s[i - 1]) {
        if (s[i - 1] != 'A' && s[i + 1] != 'A') s[i] = 'A';
        if (s[i - 1] != 'B' && s[i + 1] != 'B') s[i] = 'B';
        if (s[i - 1] != 'C' && s[i + 1] != 'C') s[i] = 'C';
        ans++;
      }
    }
    if (s[a - 1] == s[a - 2]) {
      if (s[a - 2] != 'A') s[a - 1] = 'A';
      if (s[a - 2] != 'B') s[a - 1] = 'B';
      if (s[a - 2] != 'C') s[a - 1] = 'C';
      ans++;
    }
    cout << ans << endl << s;
    return 0;
  }
  for (int i = 0; i <= a - 1; i++) {
    if (i % 2 == 0 && s[i] != 'A') {
      ans1++;
    }
    if (i % 2 == 1 && s[i] != 'B') {
      ans1++;
    }
    if (i % 2 == 0 && s[i] != 'B') {
      ans2++;
    }
    if (i % 2 == 1 && s[i] != 'A') {
      ans2++;
    }
  }
  if (ans1 < ans2) {
    cout << ans1 << endl;
    for (int i = 1; i <= a; i++) {
      if (i % 2 == 0)
        cout << 'B';
      else
        cout << 'A';
    }
  } else {
    cout << ans2 << endl;
    for (int i = 1; i <= a; i++) {
      if (i % 2 == 0)
        cout << 'A';
      else
        cout << 'B';
    }
  }
}
