#include <cstdio>
#include <queue>
#include <cstring>
#define MAXN 1001
using namespace std;
queue < pair<int, int> > q;
int dx[4] = {-1, 0, 1, 0};
int dy[4] = {0, 1, 0, -1};
bool wall[MAXN][MAXN], seen[MAXN][MAXN];
int n, m, dragonDistance[MAXN][MAXN], startX, startY, stopX, stopY;
inline bool ok(int x, int y){
    if(x < 1 || x > n || y < 1 || y > m) return 0;
    if(seen[x][y] || wall[x][y]) return 0;
    return 1;
}
void dragonBFS(){
    int nextRow, nextCol, row, col, i;
    while(!q.empty()){
        row = q.front().first;
        col = q.front().second;
        q.pop();
        for(i=0; i<4; ++i){
            nextRow = row + dx[i];
            nextCol = col + dy[i];
            if(ok(nextRow, nextCol)){
                dragonDistance[nextRow][nextCol] = dragonDistance[row][col] + 1;
                seen[nextRow][nextCol] = 1;
                q.push(make_pair(nextRow, nextCol));
            }
        }
    }
}
bool bfs(int dist){
    int nextRow, nextCol, i, row, col;
    while(!q.empty()) q.pop();
    memset(seen, 0, sizeof(seen));
    q.push(make_pair(startX, startY));
    seen[startX][startY] = 1;
    if(dragonDistance[startX][startY] < dist)
        return 0;
    while(!q.empty()){
        row = q.front().first;
        col = q.front().second;
        q.pop();
        for(i=0; i<4; ++i){
            nextRow = row + dx[i];
            nextCol = col + dy[i];
            if(ok(nextRow, nextCol) && dragonDistance[nextRow][nextCol] >= dist){
                seen[nextRow][nextCol] = 1;
                q.push(make_pair(nextRow, nextCol));
                if(nextRow == stopX && nextCol == stopY)
                    return 1;
            }
        }
    }
    return seen[stopX][stopY];
}
int main(){
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
    int i, j, pas = 1, ans = 0;
    char c;
    scanf("%d%d\n", &n, &m);
    for(i=1; i<=n; ++i){
        for(j=1; j<=m; ++j){
            scanf("%c", &c);
            if(c == '*') wall[i][j] = 1;
            if(c == 'D') wall[i][j] = seen[i][j] = 1, q.push(make_pair(i, j));
            if(c == 'I') startX = i, startY = j;
            if(c == 'O') stopX = i, stopY = j;
        }
        scanf("%c", &c);
    }
    dragonBFS();
    while((pas<<1) <= n && (pas<<1) <= m) pas<<=1;
    for(; pas>=1; pas>>=1)
        if(ans+pas<=n && ans+pas<=m && bfs(ans+pas))
            ans += pas;
    if(ans == 0){printf("-1");return 0;}
    printf("%d", ans);
    return 0;
}