#include <bits/stdc++.h>
using namespace std;
char chars[3] = {'A', 'B', 'C'};
int main() {
  int n, k;
  cin >> n >> k;
  string second, s1, s2;
  string ans;
  string tmp;
  cin >> second;
  char prev, prev2;
  int moves = 0, moves2 = 0;
  if (k == 2) {
    prev = second[0];
    s1.push_back(prev);
    prev2 = second[0] == 'A' ? 'B' : 'A';
    s2.push_back(prev2);
    moves2++;
    for (int i = 1; i < n; i++) {
      if (second[i] == prev) {
        moves++;
        prev = (second[i] == 'A' ? 'B' : 'A');
      } else
        prev = second[i];
      s1.push_back(prev);
      if (second[i] == prev2) {
        moves2++;
        prev2 = (second[i] == 'A' ? 'B' : 'A');
      } else
        prev2 = second[i];
      s2.push_back(prev2);
    }
    if (moves < moves2) {
      cout << moves << endl << s1 << endl;
    } else
      cout << moves2 << endl << s2 << endl;
    return 0;
  } else {
    prev = second[0];
    for (int i = 1; i < n; i++) {
      if (second[i] == second[i - 1]) {
        for (int j = 0; j < 3; j++) {
          if (i + 1 < n) {
            if (chars[j] != second[i - 1] && chars[j] != second[i + 1]) {
              moves++;
              prev = chars[j];
              second[i] = chars[j];
              break;
            }
          } else {
            if (chars[j] != second[i - 1]) {
              moves++;
              prev = chars[j];
              second[i] = chars[j];
              break;
            }
          }
        }
      }
    }
  }
  cout << moves << endl;
  cout << second << endl;
  return 0;
}
