#include <bits/stdc++.h>
using namespace std;
const long long maxn = 1010, add = 1000;
long long n, k, dp[maxn][maxn * 2];
string s;
int main() {
  scanf("%lld%lld", &n, &k);
  cin >> s;
  s = " " + s;
  dp[0][add] = -1;
  for (int i = 1; i <= n; i++)
    for (int j = add - k + (i < n); j <= add + k - (i < n); j++) {
      if ((s[i] == 'W' || s[i] == '?') && dp[i - 1][j - 1]) dp[i][j] = 1;
      if ((s[i] == 'L' || s[i] == '?') && dp[i - 1][j + 1]) dp[i][j] = 3;
      if ((s[i] == 'D' || s[i] == '?') && dp[i - 1][j]) dp[i][j] = 2;
    }
  if (dp[n][add + k] == 0 && dp[n][add - k] == 0) {
    puts("NO");
    return 0;
  }
  int j = (dp[n][add + k] == 0 ? add - k : add + k);
  for (int i = n; i >= 1; i--)
    if (dp[i][j] == 1)
      s[i] = 'W', j--;
    else if (dp[i][j] == 3)
      s[i] = 'L', j++;
    else if (dp[i][j] == 2)
      s[i] = 'D';
  s.erase(0, 1);
  cout << s;
  return 0;
}
