#include <bits/stdc++.h>
using namespace std;
const int z = 1005;
string s;
bool dp[1010][2010];
int par[1010][2010];
int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int n, k;
  cin >> n >> k;
  cin >> s;
  dp[0][z] = 1;
  for (int i = 0; i < n; i++) {
    for (int j = -k + 1; j < k; j++) {
      if (!dp[i][z + j]) continue;
      if (s[i] == 'W' || s[i] == '?') {
        dp[i + 1][z + j + 1] = 1;
        par[i + 1][z + j + 1] = 1;
      }
      if (s[i] == 'D' || s[i] == '?') {
        dp[i + 1][z + j] = 1;
        par[i + 1][z + j] = 0;
      }
      if (s[i] == 'L' || s[i] == '?') {
        dp[i + 1][z + j - 1] = 1;
        par[i + 1][z + j - 1] = -1;
      }
    }
  }
  if (dp[n][z + k]) {
    int p = n;
    int w = z + k;
    while (p > 0) {
      int d = par[p][w];
      p--;
      w -= d;
      if (d == 1) {
        s[p] = 'W';
      }
      if (d == 0) {
        s[p] = 'D';
      }
      if (d == -1) {
        s[p] = 'L';
      }
    }
    cout << s << endl;
  } else if (dp[n][z - k]) {
    int p = n;
    int w = z - k;
    while (p > 0) {
      int d = par[p][w];
      p--;
      w -= d;
      if (d == 1) {
        s[p] = 'W';
      }
      if (d == 0) {
        s[p] = 'D';
      }
      if (d == -1) {
        s[p] = 'L';
      }
    }
    cout << s << endl;
  } else {
    cout << "NO" << endl;
  }
  return 0;
}
