[ACM] Common Code Handler

#include <bits/stdc++.h>

// flags
#define FILE "alarm"
#define USE_FREOPEN 1
#define USE_LONG 0
#define USE_IOSOPT 0

// typedefs
#if USE_LONG
typedef int64_t ll;
typedef uint64_t ull;
#else
typedef int32_t ll;
typedef uint32_t ull;
#endif

// links
#define rl double
#define pb push_back
#define mp make_pair
#define fi first
#define f first
#define x first
#define se second
#define s second
#define y second
#define rm erase
#define ins insert
#define sz size
#define elsif else if
#define next continue
#define xb pop_back
#define hset unordered_set
#define hmap unordered_map

// macros
#define rs(a) resize((a))
#define p(a, b) pair < a, b >
#define sq(x) (x * x)
#define lsq(x) (x * 1ll * x)
#define unless(a) if(!(a))
#define skip(a) if(a) next;
#define fail(a) if(a) break;
#define skipn(a) unless(a) next;
#define failn(a) unless(a) break;
#define rev(a) reverse(a.begin(), a.end())
#define ord(a) sort(a.begin(), a.end())
#define printv(a) { for(auto ___cur___ : a) { cout << ___cur___ << ' '; }; cout << endl; }
#define printd(a) { for(auto ___cur___ : a) { cerr << ___cur___ << ' '; }; cerr << endl; }
#define die(a) \
{ \
cout << (a) << endl; \
exit(0); \
}

using namespace std;


const size_t $MAXN = (ull) (2000);
const char *$SIGNATURE[] = {"b9", "91", "af", "fc",
                            "fb", "24", "db", "04",
                            "76", "fe", "95", "76",
                            "b9", "03", "95", "2e"};
const ull $MOD = (const ull) (1e9 + 7);

ll nextInt( )
{
    ll d;
    cin >> d;
    return d;
}

string nextString( )
{
    string d;
    cin >> d;
    return d;
}

char nextChar( )
{
    char d;
    cin >> d;
    return d;
}

bool isPair(char l, char r)
{
    return (
            l == '(' && r == ')' or
                        l == '[' && r == ']'
    );
}

string slurp(string filename)
{
    ifstream in(filename);
    stringstream str;
    str << in.rdbuf( );
    return str.str( );
}


vector < string > split(const string &hay, const char &delim, const char &delim2 = '\0')
{
    vector < string > answer;
    string buffer;
    for(auto chr : hay)
    {
        if(chr == delim || chr == delim2)
        {
            answer.pb(buffer);
            buffer = "";
        } else
            buffer.pb(chr);
    }
    answer.pb(buffer);
    return answer;
}

inline bool isEven(const string &number)
{
    char last = (*number.rbegin( )) - '0';
    return (last % 2 == 0);
}


string operator*(string a, int b)
{
    string res = "";
    while(b--)
        res += a;
    return res;
}

bool isPali(const string &a)
{
    ll n = (ll) a.sz( );
    for(int i = 0; i < (ll) n; i++)
        if(a[i] != a[n - i - 1])
            return 0;
    return 1;
}

ll countPairs(ll n)
{
    return
            n * (n + 1)
            / 2;
}

ll makeNumPair(ll a, ll b)
{
    return a * 10000 + b;
}

string getStringOrInt( )
{
    return (rand( ) % 2 ? "string" : 0);
}

struct trio {
    ll a, b, c;
};

string toLower(string src)
{
    string tmp = src;
    transform(tmp.begin( ), tmp.end( ), tmp.begin( ), ::tolower);
    return tmp;
}

void solve( );

int main( )
{
    // ios{
#if USE_IOSOPT
    ios_base::sync_with_stdio(false);
    cin.tie(0);
#endif
#if USE_FREOPEN
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    solve( );
    return 0;
}

bool mx[$MAXN][$MAXN];

p(ll, ll) spos = {-1, -1};
ll k;
ll n, m;

bool canGo(const p(ll, ll) & pt)
{
    if(pt.fi >= n || pt.se >= m)
        return false;
    if(pt.fi < 0 || pt.se < 0)
        return false;

    return (mx[pt.x][pt.y]);
}


bool checkPath(const string & path)
{
    ll x = 0, y = 0;
    if(path.sz( ) != k)
        return 0;
    for(auto ch : path)
    {
        switch(ch)
        {
            case 'D':
                x++;
                break;
            case 'U':
                x--;
                break;
            case 'L':
                y--;
                break;
            case 'R':
                y++;
                break;
            default:
                break;
        }
    }

    if(x != 0 || y != 0)
        return 0;
    return 1;
}


void dfs(const p(ll, ll) & v, const string & way = "")
{
    if(way.sz( ) > k)
        return;
    if(checkPath(way))
    die(way);
    if(canGo({v.fi + 1, v.se}))
        dfs({v.fi + 1, v.se}, way + "D");
    if(canGo({v.fi, v.se - 1}))
        dfs({v.fi, v.se - 1}, way + "L");
    if(canGo({v.fi, v.se + 1}))
        dfs({v.fi, v.se + 1}, way + "R");
    if(canGo({v.fi - 1, v.se}))
        dfs({v.fi - 1, v.se}, way + "U");
}

void solve( )
{
    cin >> n >> m >> k;

    assert(!(k & 1));

    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < m; j++)
        {
            char c;
            cin >> c;
            if(c == '.')
                mx[i][j] = 1;
            if(c == 'X')
            {
                mx[i][j] = 1;
                spos = {i, j};
            }
        }
    }

    dfs(spos);

    die("IMPOSSIBLE\n");
}