#include <queue>
#include <fstream>

using namespace std;

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

const int Nmax = 1005;
char mat[Nmax][Nmax];
int matd[Nmax][Nmax], matver[Nmax][Nmax];///matrice cu distantele pana la cel mai apropiat dragon din fiecare celula a temnitei
int dirl[] = {1, 0,-1, 0};
int dirc[] = {0, 1, 0,-1};
int n, m, l, c, lstart, cstart, lfinal, cfinal;

queue <pair <int, int>> qd;
void dist_drag()
{
    int i;

    while(!qd.empty())
    {
        int lc = qd.front().first, cc = qd.front().second;
        for(i = 0; i < 4; i++)
        {
            int lvec = lc + dirl[i], cvec = cc + dirc[i];
            if((1 <= lvec && lvec <= n) and (1 <= cvec && cvec <= m) and mat[lvec][cvec] != '*' and mat[lvec][cvec] != 'D' && !matd[lvec][cvec])
                matd[lvec][cvec] = matd[lc][cc] + 1, qd.push({lvec, cvec});
        }
        qd.pop();
    }
}

bool ver(int dist)
{
    int i;
    queue <pair <int, int>> q;

    for(l = 1; l <= n; l++)
        for(c = 1; c <= m; c++)
            matver[l][c] = 0;

    q.push({lstart, cstart});
    while(!q.empty())
    {
        int lc = q.front().first, cc = q.front().second;
        if(lc == lfinal && cfinal == cc)
            return true;
        for(i = 0; i < 4; i++)
        {
            int lvec = lc + dirl[i], cvec = cc + dirc[i];
            if((1 <= lvec && lvec <= n) and (1 <= cvec && cvec <= m) and matd[lvec][cvec] >= dist && !matver[lvec][cvec])
                matver[lvec][cvec] = matver[lc][cc] + 1, q.push({lvec, cvec});
        }
        q.pop();
    }

    if(matver[lfinal][cfinal])
        return true;
    return false;
}




int main()
{
    fin >> n >> m;
    fin.get();
    for(l = 1; l <= n; l++)
    {
        for(c = 1; c <= m; c++)
        {
            fin.get(mat[l][c]);
            if(mat[l][c] == 'D')
                qd.push({l, c});
            if(mat[l][c] == 'I')
                lstart = l, cstart = c;
            if(mat[l][c] == 'O')
                lfinal = l, cfinal = c;
        }
        fin.get();
    }

    dist_drag();



    int st = 0, dr = 2005, ans;
    while(st < dr)
    {
        int mij = (st + dr) >> 1;
        if(!ver(mij))
            dr = mij - 1;
        else
            st = mij + 1, ans = mij;
    }
    fout << ans;


    return 0;
}