#include <fstream>
#include <queue>
#include <cstring>
using namespace std;
#define DIM 1001

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

struct Cel{ int i, j;}Start, Finish;

const int di[] = {-1, 0, 1, 0};
const int dj[] = {0, 1, 0, -1};

int n, m, b[DIM][DIM];
char a[DIM][DIM];
bool Ex[DIM][DIM];

queue <Cel> Q;

void Read();
void BFS();
bool BFSCheck(int x);
void Solve();
bool Ok(int i, int j);

int main()
{
    Read();
    BFS();
    Solve();
    fin.close();
    fout.close();
    return 0;
}

void Read()
{
    fin >> n >> m;
    fin.get();
    Cel Dragon;
    for (int i = 1; i <=n; ++i)
        for (int j = 1; j <= m; ++j)
        {
            fin >> a[i][j];
            if (a[i][j] == 'I') Start.i = i, Start.j = j;
            if (a[i][j] == 'D') Dragon.i = i, Dragon.j = j, Q.push(Dragon);
            if (a[i][j] == 'O') Finish.i = i, Finish.j = j;
        }
};

void Solve()
{
    for (int i = b[Start.i][Start.j]; i >= 1; i--)
        if (BFSCheck(i) == true)
        {
            fout << i;
            return;
        }
    fout << -1;
};

bool BFSCheck(int x)
{
    memset(Ex, 0, sizeof(Ex));
    Cel Ac;
    int i, j, iv, jv;
    Q.push(Start);
    while (!Q.empty())
    {
        Ac = Q.front(), Q.pop();
        i = Ac.i, j = Ac.j;
        for (int dir = 0; dir < 4; dir++)
        {
            iv = i + di[dir]; jv = j + dj[dir];
            if (b[iv][jv] >= x && Ex[iv][jv] == false && Ok(iv, jv))
            {
                Ex[iv][jv] = true;
                Ac.i = iv, Ac.j = jv;
                Q.push(Ac);
                if (iv == Finish.i && jv == Finish.j)
                    return true;
            }
        }
    }
    return false;
};

void BFS()
{
    Cel Ac;
    int i, j, iv, jv;
    while (!Q.empty())
    {
        Ac = Q.front(), Q.pop();
        i = Ac.i, j = Ac.j;
        for (int dir = 0; dir < 4; dir++)
        {
            iv = i + di[dir], jv = j + dj[dir];
            if (Ok(iv, jv) && b[iv][jv] == 0)
            {
                b[iv][jv] = b[i][j] + 1;
                Ac.i = iv, Ac.j = jv;
                Q.push(Ac);
            }
        }
    }
};

bool Ok(int i, int j)
{
    if (i < 1 || j < 1 || i > n || j > m || a[i][j] == 'D' || a[i][j] == '*') return false;
    return true;
};