#include <fstream>
#include <deque>
#define DIM 1002

using namespace std;

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

int i, j, n, m, st, dr, ok, a[DIM][DIM], b[DIM][DIM], xi, yi, xf, yf, xc, yc, xin, yin, mid, okk;

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

struct abc
{
    int x, y;
}aux;

deque <abc> c;

char ch;

int check(int x, int y)
{
    if(x > n || x < 1 || y > m || y < 1)
        return 0;
    return 1;
}

int main()
{
    f>>n>>m;
    for(i = 1; i <= n; ++ i)
        for(j = 1; j <= m; ++ j)
        {
            f>>ch;
            if(ch == '*')
                a[i][j] = -1;
            if(ch == 'D')
            {
                aux.x = i;
                aux.y = j;
                c.push_back(aux);
                a[i][j] = 1;
            }
            if(ch == 'I')
            {
                xin = i;
                yin = j;
            }
            if(ch == 'O')
            {
                xf = i;
                yf = j;
            }
        }

    while(!c.empty())
    {
        aux = c.front();
        xi = aux.x;
        yi = aux.y;
        for(i = 0;i <= 3; ++ i)
        {
            xc = xi + dx[i];
            yc = yi + dy[i];
            if(a[xc][yc] == 0 && check(xc, yc))
            {
                a[xc][yc] = a[xi][yi] + 1;
                aux.x = xc;
                aux.y = yc;
                c.push_back(aux);
            }
        }
        c.pop_front();
    }

    st = 1;
    dr = max(n, m);

    while(st <= dr)
    {
        mid = (st + dr) / 2;
        c.clear();
        aux.x = xin;
        aux.y = yin;
        c.push_back(aux);
        ok = 0;
        while(!c.empty() && ok == 0)
        {
            aux = c.front();
            xi = aux.x;
            yi = aux.y;
            for(i = 0; i <= 3; ++ i)
            {
                xc = xi + dx[i];
                yc = yi + dy[i];
                if(a[xc][yc] >= mid && check(xc, yc) && b[xc][yc] != mid)
                {
                    b[xc][yc] = mid;
                    aux.x = xc;
                    aux.y = yc;
                    c.push_back(aux);
                    if(xc == xf && yc == yf)
                        ok = 1;
                }
            }
            c.pop_front();
        }
        if(ok == 1)
        {
            st = mid + 1;
            okk = 1;
        }
        else
            dr = mid - 1;
    }
    if(dr - 1 >= 0)
        g<<dr-1;
    else
        g<<-1;

    /*for(i = 1;i <= n; ++ i)
    {
        for(j = 1;j <= m; ++ j)
            g<<a[i][j]<<" ";
        g<<'\n';
    }*/

    return 0;
}