#include <bits/stdc++.h>
using namespace std;
long long dp[1001][2010];
void print(long long n, long long k) {
  if (n == 0) return;
  print(n - 1, k - dp[n][k]);
  if (dp[n][k] == 1) cout << "W";
  if (dp[n][k] == -1) cout << "L";
  if (dp[n][k] == 0) cout << "D";
}
signed main(void) {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n, k;
  cin >> n >> k;
  string s;
  cin >> s;
  for (__typeof(1001) i = (0) - ((0) > (1001)); i != (1001) - ((0) > (1001));
       i += 1 - 2 * ((0) > (1001)))
    for (__typeof(2010) j = (0) - ((0) > (2010)); j != (2010) - ((0) > (2010));
         j += 1 - 2 * ((0) > (2010)))
      dp[i][j] = -2;
  dp[0][1000] = 2;
  for (__typeof(n) i = (0) - ((0) > (n)); i != (n) - ((0) > (n));
       i += 1 - 2 * ((0) > (n))) {
    for (__typeof(2010) j = (0) - ((0) > (2010)); j != (2010) - ((0) > (2010));
         j += 1 - 2 * ((0) > (2010))) {
      if (abs(j - 1000) >= k || dp[i][j] == -2) continue;
      if (s[i] == 'W' || s[i] == '?') dp[i + 1][j + 1] = 1;
      if (s[i] == 'L' || s[i] == '?') dp[i + 1][j - 1] = -1;
      if (s[i] == 'D' || s[i] == '?') dp[i + 1][j] = 0;
    }
  }
  if (dp[n][k + 1000] == -2 && dp[n][1000 - k] == -2) {
    cout << "NO" << '\n';
    return 0;
  }
  if (dp[n][k + 1000] != -2)
    print(n, k + 1000);
  else
    print(n, 1000 - k);
}
