#include<bits/stdc++.h>
using namespace std;
#define nl "\n"
#define fi first
#define se second
#define pb push_back
#define ll long long
#define ull unsigned ll
#define RV  return void
// #define inf 2000000000
#define sz(x) int(x.size())
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define Mini(x) *min_element(all(x))
#define Maxi(x) *max_element(all(x))
#define fixed(n) fixed << setprecision(n)
#define ceil(w, m) (((w) / (m)) + ((w) % (m) ? 1 : 0))
#define cin(v) for (auto&i:v) cin >> i;
#define cout(v) for (auto&i:v) cout << i << " ";
#define clr(memo, x) memset(memo, x, sizeof memo)
#define updmin(a, b) a = min(a, b)
#define updmax(a, b) a = max(a, b)
#define vi vector < int >
#define vl vector < ll >
#define vc vector < char >
#define vs vector < string >
#define v2i vector < vector < int > >
#define v2l vector < vector < int > >
#define seti set < int >
#define setl set < ll >
#define mapii map < int , int >
#define mapll map < ll , ll >
#define mapli map < ll , int >
#define mapci map < char , int >
#define mapsi map < string , int >
#define pll pair < ll , ll >
#define pii pair < int , int >
#define range(l,r,x) for(int i=l ; i < r ; i+=x)
#define FastCode ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
vector < string > ternary= {"NO\n" , "YES\n"};

void  Zainab(){
            #ifndef ONLINE_JUDGE
              freopen("input.txt", "r", stdin);
              freopen("output.txt", "w", stdout);
            #endif
}


/*================================  solution  ================================ */

const int N = 1e3+5;
char arr[N][N];


int dx[] = {1 , -1 , 0 , 0};
int dy[] = {0 , 0 , 1 , -1};
char C[] = {'D' , 'U' , 'R' , 'L'};

bool vis[N][N];
int n , m;
string path , ans = "-1";



bool valid (int x , int y  ){
    return x >= 0 && x < n && y >= 0 && y < m && arr[x][y] != '#' && !vis[x][y];
}


void bfs(int ax  , int ay , int bx , int by){

    queue < pair < int , int > > q;
    q.push({ax , ay});
    vis[ax][ay] = 1;

    while(!q.empty()){
        auto p = q.front();
        q.pop();
        int x = p.fi , y = p.se;
        for(int i =0 ; i < 4 ; i++){
            int nx = x + dx[i] , ny = y + dy[i];

            if(valid(nx , ny)){
                vis[nx][ny] = 1;
                path += C[i];
                q.push({nx,ny});
                if(nx == bx && ny == by){
                    // cout << x << " " << y << " " << nx << " " << ny << nl;
                    // cout << path << nl;

                    path.pop_back();
                    if(sz(path) < sz(ans) or ans =="-1"){
                        ans = path ;
                        path="";
                    }

                }

            }
        }
    }
}



void myCode(){



    cin >> n >> m ;
    int aX  , aY , bX , bY;
    for(int i =0 ;  i < n ; i++){
        for(int j =0 ; j < m ; j++){
            cin >> arr[i][j];

            if(arr[i][j]=='A')
                aX = i ,  aY = j;
            else if(arr[i][j]=='B')
                bX = i , bY = j;

        }
    }


    bfs(aX , aY , bX , bY);
    cout << sz(ans) << nl;
    cout << ans ;
}


int main(){

                                FastCode ;
                     Zainab() ;

            int testCase=1;
                // cin >> testCase ;
            for(int i=1 ; i<= testCase ; i++){
                //  cout << "Case #" << i << ": ";
                myCode();
            }


    return 0;
}