#include <bits/stdc++.h>
using namespace std;
int n, k, win, lose;
bool dp[1005][2010];
string s;
void solve(int idx, int d) {
  if (idx == n && abs(d) == k) cout << s, exit(0);
  if (dp[idx][d + n] || abs(d) >= k || idx == n) return;
  dp[idx][d + n] = 1;
  if (s[idx] == '?') {
    s[idx] = 'W', solve(idx + 1, d + 1);
    s[idx] = 'L', solve(idx + 1, d - 1);
    s[idx] = 'D', solve(idx + 1, d);
    s[idx] = '?';
  } else if (s[idx] == 'W')
    solve(idx + 1, d + 1);
  else if (s[idx] == 'L')
    solve(idx + 1, d - 1);
  else
    solve(idx + 1, d);
}
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> n >> k >> s;
  solve(0, 0);
  cout << "NO" << endl;
  return 0;
}
