#include <bits/stdc++.h>
using namespace std;
long long n, k;
string s, ans = "";
int main() {
  scanf("%ld%ld", &n, &k);
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    if ('z' - s[i] >= s[i] - 'a') {
      if (k <= 'z' - s[i]) {
        ans += (char)(s[i] + k);
        cout << ans;
        for (int j = i + 1; j < s.size(); j++) printf("%c", s[j]);
        return 0;
      } else {
        ans += 'z';
        k -= ('z' - s[i]);
      }
    } else {
      if (k <= s[i] - 'a') {
        ans += (char)(s[i] - k);
        cout << ans;
        for (int j = i + 1; j < s.size(); j++) printf("%c", s[j]);
        return 0;
      } else {
        ans += 'a';
        k -= (s[i] - 'a');
      }
    }
  }
  printf("-1\n");
}
