#include <fstream>
#include <queue>
#include <cstring>

using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");

int R, C, x1, y1, x2, y2;
int matrixDist[1005][1005];
int dx[] = {-1, 0, 1, 0}, dy[] = {0, 1, 0, -1};
bool vis[1005][1005], avalabile[1005][1005];
queue < pair < int, int > > Q;

void InitLee()
{
    while(!Q.empty())
    {
        int x = Q.front().first;
        int y = Q.front().second;
        Q.pop();

        for(int i = 0; i < 4; i++)
        {
            int xx = x + dx[i];
            int yy = y + dy[i];
            if(xx && yy && xx <= R && yy <= C)
                if(vis[xx][yy] == false && avalabile[xx][yy] == false)
                {
                    vis[xx][yy] = true;
                    matrixDist[xx][yy] = matrixDist[x][y] + 1;
                    Q.push(make_pair(xx, yy));
                }
        }
    }
}

bool Lee(int lmt)
{
    if(matrixDist[x1][y1] < lmt)
        return false;

    memset(vis, 0, sizeof(vis));
    vis[x1][y1] = true;
    Q.push(make_pair(x1, y1));

    while(!Q.empty())
    {
        int x = Q.front().first;
        int y = Q.front().second;
        Q.pop();

        for(int i = 0; i < 4; i++)
        {
            int xx = x + dx[i];
            int yy = y + dy[i];

            if(xx && yy && xx <= R && yy <= C)
                if(matrixDist[xx][yy] >= lmt && vis[xx][yy] == false && avalabile[xx][yy] == false)
                {
                    vis[xx][yy] = true;
                    Q.push(make_pair(xx, yy));

                    if(xx == x2 && yy == y2)
                    {
                        while(!Q.empty())
                            Q.pop();

                        return true;
                    }
                }
        }
    }

    return false;
}

int main()
{
    fin >> R >> C;

    char s[1005];
    for(int i = 1; i <= R; i++)
    {
        fin >> s;
        for(int j = 0; j < C; j++)
        {
            if(s[j] == '*')
                avalabile[i][j + 1] = true;
            else if(s[j] == 'I')
                x1 = i, y1 = j + 1;
            else if(s[j] == 'O')
                x2 = i, y2 = j + 1;
            else if(s[j] == 'D')
                vis[i][j + 1] = true, Q.push(make_pair(i, j + 1));
        }
    }

    InitLee();

    int st = 0, dr = 2000, mid, sol = -1;
    while(st <= dr)
    {
        mid =(st + dr) / 2;

        if(Lee(mid) == true)
        {
            sol = mid;
            st = mid + 1;
        }
        else
            dr = mid - 1;
    }

    fout << sol;

    return 0;
}