#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e3 + 5;
inline int _(int x) { return x + maxn; }
int n, m;
char s[maxn];
char ans[maxn];
char f[maxn][(maxn << 1) + 5];
bool dp[maxn][(maxn << 1) + 5];
int main() {
  scanf("%d%d", &n, &m);
  scanf("%s", s);
  dp[0][_(0)] = 1;
  for (int i = (0); i < (n); ++i)
    for (int j = (-m); j <= (m); ++j)
      if (dp[i][_(j)]) {
        int k = j;
        if (s[i] == 'W' || s[i] == '?') {
          k = j + 1;
          if (abs(k) < m || i == n - 1) {
            dp[i + 1][_(k)] = true;
            f[i + 1][_(k)] = 'W';
          }
        }
        if (s[i] == 'L' || s[i] == '?') {
          k = j - 1;
          if (abs(k) < m || i == n - 1) {
            dp[i + 1][_(k)] = true;
            f[i + 1][_(k)] = 'L';
          }
        }
        if (s[i] == 'D' || s[i] == '?') {
          k = j;
          if (abs(k) < m || i == n - 1) {
            dp[i + 1][_(k)] = true;
            f[i + 1][_(k)] = 'D';
          }
        }
      }
  if (dp[n][_(m)]) {
    for (int i = n, j = m; i; --i) {
      ans[i - 1] = f[i][_(j)];
      if (f[i][_(j)] == 'W')
        --j;
      else if (f[i][_(j)] == 'L')
        ++j;
    }
    printf("%s\n", ans);
    return 0;
  }
  if (dp[n][_(-m)]) {
    for (int i = n, j = -m; i; --i) {
      ans[i - 1] = f[i][_(j)];
      if (f[i][_(j)] == 'W')
        --j;
      else if (f[i][_(j)] == 'L')
        ++j;
    }
    printf("%s\n", ans);
    return 0;
  }
  puts("NO");
  return 0;
}
