#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  map<long long, long long> dp[n + 1];
  dp[0][0] = 1;
  for (long long i = 1; i <= n; i++) {
    for (auto it : dp[i - 1]) {
      if (it.first == -k || it.first == k) continue;
      if (s[i - 1] == 'D' || s[i - 1] == '?') dp[i][it.first] = 1;
      if (s[i - 1] == 'L' || s[i - 1] == '?') dp[i][it.first - 1] = 1;
      if (s[i - 1] == 'W' || s[i - 1] == '?') dp[i][it.first + 1] = 1;
    }
  }
  if (dp[n][-k] | dp[n][k]) {
    string ans;
    long long cnt = k;
    if (dp[n][-k]) cnt = -k;
    for (long long i = n; i >= 1; i--) {
      if (s[i - 1] != '?') {
        ans.push_back(s[i - 1]);
        if (s[i - 1] == 'W')
          cnt--;
        else if (s[i - 1] == 'L')
          cnt++;
        continue;
      }
      if (cnt + 1 != k && dp[i - 1][cnt + 1]) {
        ans.push_back('L');
        cnt++;
      } else if (cnt != k && dp[i - 1][cnt]) {
        ans.push_back('D');
      } else {
        cnt--;
        ans.push_back('W');
      }
    }
    reverse(ans.begin(), ans.end());
    cout << ans << '\n';
  } else
    cout << "NO" << '\n';
}
