#include <iostream>
#include <fstream>

using namespace std;

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

short int dl[] = {-1,0,1,0};
short int dc[] = {0,1,0,-1};

struct element
{
    int l;
    int c;
};

int n,m;
char a[1002][1002];

int b[1002][1002];
int c[1002][1002];
element q[1002*1002];
int st = 0,dr = -1,xs,ys,xf,yf;

void Golire()
{
    for (int i=1; i<= n; i++)
    {
        for (int j=1; j<=m; j++)
        {
            c[i][j] = 0;
        }
    }
}

void Bordare()
{
    int i,j;
    for (i=0; i<=n+1; i++)
    {
        a[i][0] = a[i][m+1] = -2;
    }
    for (j=0; j<=m+1; j++)
    {
        a[0][j] = a[n+1][j] = -2;
    }
}

bool exista_drum(int val)
{
    element x,y;
    st = 0;
    dr = -1;
    Golire();
    c[xs][ys] = 1;
    q[++dr] = (element){xs,ys};
    while (st <= dr)
    {
        x = q[st++];
        for (int k=0; k<4; k++)
        {
            y.l = x.l + dl[k];
            y.c = x.c + dc[k];
            if ((b[y.l][y.c] >= val || b[y.l][y.c] == -1) && c[y.l][y.c] == 0)
            {
                c[y.l][y.c] = 1 + c[x.l][x.c];
                q[++dr] = y;
            }
        }
    }
    return (c[xf][yf] != 0);
}

int Cautare()
{
    int st = 0,dr = 2000,mij,val = -1;
    while (st < dr)
    {
        mij = (st+dr)/2;
        if (exista_drum(mij))
        {
            st = mij+1;
            val = mij;
        }
        else
        {
            dr = mij;
        }
    }
    return val;
}

void Lee()
{
    element x,y;
    b[xs][ys] = 1;
    while (st <= dr)
    {
        x = q[st++];
        for (int k=0; k<4; k++)
        {
            y.l = x.l + dl[k];
            y.c = x.c + dc[k];
            if (b[y.l][y.c] == 0 && a[y.l][y.c] == '.')
            {
                b[y.l][y.c] = b[x.l][x.c] + 1;
                q[++dr] = y;
            }
        }
    }
}

int main()
{
    int i,j;
    in >> n >> m;
    Bordare();
    for (i=1; i<=n; i++)
    {
        in >> (1+a[i]);
        for (j=1; j<=m; j++)
        {
            if (a[i][j] == 'I')
            {
                xs = i;
                ys = j;
            }
            if (a[i][j] == 'O')
            {
                xf = i;
                yf = j;
            }
            if (a[i][j] == 'D')
            {
                q[++dr] = (element){i,j};
            }
            if (a[i][j] == '*')
            {
                b[i][j] = -2;
            }
        }
    }
    Lee();
    b[xs][ys] = -1;
    b[xf][yf] = -1;
    /*for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            cout << b[i][j] << " ";
        }
        cout << endl;
    }*/
    out << Cautare();
    return 0;
}