#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");
char v[1001][1001];
int cost[1001][1001];

int finalx=0,finaly=0;
int startx=0,starty=0;
int r,c;
bool visited[1001][1001];
bool checkPath(int x,int y,int expectedCost)
{
    if ((x<0) ||(x>r)) return false;
    if ((y<0) ||(y>c)) return false;
    if (cost[x][y] < expectedCost) return false;

    if (visited[x][y]) return false;

    if ((x==finalx)&&(y==finaly))
    {
        return true;
    }

    visited[x][y] = true;
    return checkPath(x-1,y,expectedCost) ||checkPath(x+1,y,expectedCost)||checkPath(x,y+1,expectedCost)||checkPath(x,y-1,expectedCost);
}

int main()
{

    int res=-1;
    fin >> r >> c;
    char endline;
    //fin >> endline;

    for (int i=0; i<r; i++)
    {


        for (int j=0; j<c; j++)
        {
            fin >> v[i][j];
        }

        //fin >> endline;
    }




    for (int i=0; i<r; i++)
        for (int j=0; j<c; j++)
            cost[i][j]=1000000;

    vector< pair<int , int > > updPoints;
    vector< pair<int , int > > updPointsNew;
    updPoints.clear();

    for (int i=0; i<r; i++)
    {
        for (int j=0; j<c; j++)
        {
            //cout << v[i][j];
            if (v[i][j] == 'D')
            {
                updPoints.push_back(make_pair(i,j));
                cost[i][j]=0;
            }

            if (v[i][j] == '*')
            {
                cost[i][j]=-1;
            }

            if (v[i][j] == 'O')
            {
                finalx = i;
                finaly = j;
            }

            if (v[i][j] == 'I')
            {
                startx = i;
                starty = j;
            }

        }

        //cout << endl;
    }
    //cout <<"D number:"<< updPoints.size()<<endl;
    bool found=true;
    while (found)
    {
        found = false;
        updPointsNew.clear();

        for (int i=0; i<updPoints.size(); i++)
        {

            for (int j=0; j<4; j++)
            {
                int x= updPoints[i].first;
                int y= updPoints[i].second;
                int dx=x;
                int dy=y;
                if (j==0) dx--;
                if (j==1) dx++;
                if (j==2) dy--;
                if (j==3) dy++;

                if (dx>r||dx<0||dy<0||dy>c) continue;

                if (cost[dx][dy] >  cost[x][y]+1)
                {
                    cost[dx][dy] =  cost[x][y]+1;
                    updPointsNew.push_back(make_pair(dx,dy));
                    found  = true;
                }
            }
        }
        swap(updPointsNew,updPoints);
    }
    int rr=1000000;
    int ll=0;

    while (ll<rr)
    {
        int mm = (rr + ll) / 2 + 1;

        for (int i=0; i<r; i++)
        {
            for (int j=0; j<c; j++)
            {
                visited[i][j] =false;
              //  fout << cost[i][j]<< " ";
            }
            //fout << endl;
        }
        //cout << "rr:"<<rr<<","<<"ll:"<<ll<<endl;
        if (checkPath(startx,starty,mm))
        {
            //cout << "check ok" << mm <<endl;
            res=mm;
            ll= mm+1;
        }
        else
        {
            //cout << "check failed"<< mm << endl;
            rr= mm-1;
        }

        swap(updPointsNew,updPoints);
    }


    fout << res;
}