Cycle In Maze

#include <bits/stdc++.h>
using namespace std;
typedef pair<int, int> ii;

const int MAX = 1010;
const int INF = 0x3f3f3f3f;

int n, m, k;
string gr[MAX];

int main() {
  cin.tie(0)->sync_with_stdio(0);

  cin >> n >> m >> k;

  int pi = -1, pj = -1;
  for (int i = 0; i < n; ++i) {
    cin >> gr[i];
    for (int j = 0; j < m; ++j) {
      if (gr[i][j] == 'X') {
        pi = i; pj = j;
      }
    }
  }

  if (k & 1) {
    cout << "IMPOSSIBLE\n";
    exit(0);
  }

  int tam = k/2;

  k /= 2;
  string ans = "";

  while (k--) {
    if (pi+1 <= n-1 and gr[pi+1][pj] != '*') {
      ans += "D";
      pi++;
    } else if (pj-1 >= 0 and gr[pi][pj-1] != '*') {
      ans += "L";
      pj--;
    } else if (pj+1 <= m-1 and gr[pi][pj+1] != '*') {
      ans += "R";
      pj++;
    } else if (pi-1 >= 0 and gr[pi-1][pj] != '*') {
      ans += "U";
      pi--;
    }
  }

  if (ans.size() != tam) {
    cout << "IMPOSSIBLE\n";
    exit(0);
  }

  string aux = ans;
  reverse(aux.begin(), aux.end());
  for (char &c : aux) {
    if (c == 'L') c = 'R';
    else if (c == 'R') c = 'L';
    else if (c == 'U') c = 'D';
    else if (c == 'D') c = 'U';
  }

  cout << ans << aux << '\n';
}