#include <bits/stdc++.h>
using namespace std;
void fail() {
  cout << "NO" << endl;
  exit(0);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  string ans;
  set<pair<int, int> > vis;
  function<void(int, int)> rek = [&](int i, int cur) {
    if (!vis.insert({i, cur}).second) return;
    if (i == n) {
      if (abs(cur) == k) {
        cout << ans << endl;
        exit(0);
      } else
        return;
    }
    if (abs(cur) == k) return;
    string t;
    if (s[i] != '?')
      t.push_back(s[i]);
    else
      t = "WLD";
    for (auto &c : t) {
      ans.push_back(c);
      rek(i + 1, cur + (c == 'W') - (c == 'L'));
      ans.pop_back();
    }
  };
  rek(0, 0);
  cout << "NO" << endl;
}
