#include <bits/stdc++.h>
using namespace std;
int n, k;
char s[1009];
char ans[1009];
int dp[1002][1002];
int f(int i = 0, int d = 0) {
  if (i == n) return abs(d) == k;
  int& ret = dp[i][d];
  if (ret != -1) return ret;
  if (abs(d) == k) return ret = 0;
  if (s[i] != '?') {
    ans[i] = s[i];
    if (s[i] == 'W')
      ret = f(i + 1, d + 1);
    else if (s[i] == 'L')
      ret = f(i + 1, d - 1);
    else
      ret = f(i + 1, d);
  } else {
    if (f(i + 1, d + 1)) {
      ans[i] = 'W';
      ret = 1;
    } else if (f(i + 1, d - 1)) {
      ans[i] = 'L';
      ret = 1;
    } else if (f(i + 1, d)) {
      ans[i] = 'D';
      ret = 1;
    } else
      ret = 0;
  }
  return ret;
}
int main(int argc, char* argv[]) {
  scanf("%d %d", &n, &k);
  scanf("%s", s);
  memset(dp, -1, sizeof dp);
  if (f()) {
    ans[n] = '\0';
    puts(ans);
  } else
    puts("NO");
  return 0;
}
