#include <fstream>
#include <queue>
using namespace std;

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

int mat[1010][1010], drag[1010][1010], drum_fin[1010][1010];
int r, c, nr_drag, poz=-1;

int dx[] = { 0,0,1,-1 };
int dy[] = { -1,1,0,0 };

pair<int, int> coord_drag[1010], coord_start, coord_final;
queue<pair<int, int> > coada;

void init()
{
    for(int i=1; i<=r; i++)
        for(int j=1; j<=c; j++)
            drum_fin[i][j]=0;
}

void afisare(int x[][1010])
{
    for(int i=1; i<=r; i++)
    {
        for(int j=1; j<=c; j++)
            out<<x[i][j]<<" ";
        out<<'\n';
    }
}

void captusire(int x[][1010])
{
    for (int i = 0; i <= r + 1; i++)
        x[i][0] = x[i][c + 1] = -1;

    for (int j = 0; j <= c + 1; j++)
        x[0][j] = x[r + 1][j] = -1;
}

void alg_Lee()
{
    while (!coada.empty())
    {
        int okx = coada.front().first;
        int oky = coada.front().second;
        coada.pop();

        for (int i = 0; i < 4; i++)
        {
            int x2 = okx + dx[i];
            int y2 = oky + dy[i];

            if ((drag[x2][y2] > drag[okx][oky] + 1 || drag[x2][y2] == 0) && mat[x2][y2]!=-1)
            {
                drag[x2][y2] = drag[okx][oky] + 1;
                coada.push(make_pair(x2, y2));
            }
        }
    }
}

int drum(int mij)
{
    init();
    while(!coada.empty())
        coada.pop();
    drum_fin[coord_start.first][coord_start.second]=1;
    coada.push(coord_start);

    while(!coada.empty())
    {
        int okx=coada.front().first;
        int oky=coada.front().second;
        coada.pop();

        if(okx==coord_final.first && oky==coord_final.second)
        {
            //afisare(drum_fin);
            return 1;
        }

        for(int i=0; i<4; i++)
        {
            int x2=okx+dx[i];
            int y2=oky+dy[i];

            if((drag[x2][y2]>=mij || drag[x2][y2]==0)&&(drum_fin[x2][y2]>drum_fin[okx][oky]+1 || drum_fin[x2][y2]==0))
            {
                drum_fin[x2][y2]=drum_fin[okx][oky]+1;
                coada.push(make_pair(x2,y2));
            }
        }
    }
    return 0;
}

void caut_bin(int st, int dr)
{
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(drum(mij)==1)
        {
            poz=mij;
            st=mij+1;
        }
        else dr=mij-1;
    }
}

int main()
{
    in >> r >> c;
    captusire(drag);
    captusire(drum_fin);

    for (int i = 1; i <= r; i++)
        for (int j = 1; j <= c; j++)
        {
            char x;
            in >> x;

            if (x == '.')
                mat[i][j] = 0;
            else if (x == '*')
                mat[i][j] = -1;
            else if (x == 'D')
            {
                mat[i][j] = 0;
                coord_drag[++nr_drag] = make_pair(i, j);
            }
            else if (x == 'I')
            {
                mat[i][j] = 0;
                coord_start = make_pair(i, j);
            }
            else if (x == 'O')
            {
                mat[i][j] = 0;
                coord_final = make_pair(i, j);
            }
        }

    for (int i = 1; i <= nr_drag; i++)
    {
        coada.push(make_pair(coord_drag[i].first, coord_drag[i].second));
    }

    alg_Lee();

    for (int i = 1; i <= nr_drag; i++)
    {
        drag[coord_drag[i].first][coord_drag[i].second] = 0;
    }

    //afisare(drag);
    caut_bin(0,r*c);
    out<<poz<<"\n";


    in.close();
    out.close();
    return 0;
}