C++ :

#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
int m, n;
struct node{
    int x, y;
    node(int a, int b){
        x = a; y = b;
    }
}*xm, *d;
char maze[301][301];
int dist[301][301], steps;
bool vis[301][301];
queue<node*> q;
void PUSH(int a, int b){
    if(vis[a][b] || a < 1 || b < 1 || a > m || b > n || maze[a][b] == 'S') return;
    q.push(new node(a, b));
    dist[a][b] = steps+1;
    vis[a][b] = 1;
}
int bfs(){
    memset(vis, 0, sizeof(vis));
    memset(dist, 0, sizeof(dist));
    node *cur = new node(xm->x, xm->y);
    while(!q.empty()) q.pop();
    q.push(cur);
    vis[xm->x][xm->y] = 1;
    while(!q.empty()){
        cur = q.front(); q.pop();
        steps = dist[cur->x][cur->y];
        if(cur->x == d->x && cur->y == d->y)
            return dist[d->x][d->y];

        if(maze[cur->x][cur->y] == 'L'){
            maze[cur->x][cur->y] = 'P';
            vis[cur->x][cur->y] = 0;
            PUSH(cur->x, cur->y);
        }else{
            PUSH(cur->x - 1, cur->y);
            PUSH(cur->x, cur->y - 1);
            PUSH(cur->x, cur->y + 1);
            PUSH(cur->x + 1, cur->y);
        }
    }
    return -1;
}
int main(){
    int i, j;
    while(scanf("%d%d", &m, &n) && m||n){
        for(i = 1; i <= m; i++)
            for(j = 1; j <= n; j++){
                scanf(" %c ", &maze[i][j]);
                if(maze[i][j] == 'X')
                    xm = new node(i, j);
                else if(maze[i][j] == 'D')
                    d = new node(i, j);
            }
        printf("%d\n", bfs());
    }
    return 0;
}