#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e3 + 10;
const int jyb = 1e3 + 5;
int n, k;
char str[maxn];
char s[maxn][maxn << 1];
bool f[maxn][maxn << 1];
int main() {
  cin >> n >> k;
  scanf("%s", str + 1);
  f[0][0 + jyb] = true;
  bool ans = true;
  for (int i = 1; i <= n; i++) {
    for (int j = -k + (i != n); j < k + (i == n); j++) {
      if (str[i] == 'L' || str[i] == '?') {
        if (f[i - 1][j + jyb - 1]) {
          f[i][j + jyb] = 1;
          s[i][j + jyb] = 'L';
        }
      }
      if (str[i] == 'D' || str[i] == '?') {
        if (f[i - 1][j + jyb] && i != n) {
          f[i][j + jyb] = 1;
          s[i][j + jyb] = 'D';
        }
      }
      if (str[i] == 'W' || str[i] == '?') {
        if (f[i - 1][j + jyb + 1]) {
          f[i][j + jyb] = 1;
          s[i][j + jyb] = 'W';
        }
      }
    }
  }
  ans = ans && (f[n][jyb + k] || f[n][jyb - k]);
  if (!ans) {
    printf("NO\n");
    return 0;
  }
  int now = f[n][jyb + k] ? k : -k;
  for (int i = n; i >= 1; i--) {
    str[i] = s[i][jyb + now];
    if (s[i][jyb + now] == 'W')
      now++;
    else if (s[i][jyb + now] == 'L')
      now--;
  }
  printf("%s\n", str + 1);
  return 0;
}
