#include <bits/stdc++.h>

using namespace std;

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

int n, m;
int v[1022][1022];
int w[1022][1022];
int startlin, startcol, stoplin, stopcol;

queue<pair<int,int>> coada;

int viz[1020][1020];

int di[4] = {0,0,-1,1};
int dj[4] = {1,-1,0,0};

bool verifica(int i, int j)
{
    if(i < 1 || j < 1 || i > n || j > m)
        return false;
    if(v[i][j] == -1)
        return false;
    return true;
}

void Lee()
{
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            if(v[i][j] == 0)
                v[i][j] = 1e7;
        }
    }
    while(!coada.empty())
    {
        int lin = coada.front().first;
        int col = coada.front().second;
        coada.pop();
        for(int i = 0; i < 4; i ++)
        {
            int linie_noua = lin + di[i];
            int coloana_noua = col + dj[i];
            if(verifica(linie_noua,coloana_noua) && v[lin][col] + 1 < v[linie_noua][coloana_noua])
            {
                v[linie_noua][coloana_noua] = v[lin][col] + 1;
                coada.push(make_pair(linie_noua,coloana_noua));
            }
        }
    }
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            if(v[i][j] == 1e7)
                v[i][j] = -1;
            else if(v[i][j] > 0)
                v[i][j] --;
        }
    }
}

int parcurgere(int val)
{
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            w[i][j] = 1e7;
            viz[i][j] = 0;
        }
    }
    w[startlin][startcol] = 0;
    viz[startlin][startcol] = 1;
    coada.push(make_pair(startlin,startcol));

    while(!coada.empty())
    {
        int l = coada.front().first;
        int c = coada.front().second;
        coada.pop();
        for(int i = 0; i < 4; i ++)
        {
            int lnou = l + di[i];
            int cnou = c + dj[i];
            if(verifica(lnou,cnou) && v[lnou][cnou] >= val && viz[lnou][cnou] == 0)
            {
                viz[lnou][cnou] = 1;
                w[lnou][cnou] = w[l][c];
                coada.push(make_pair(lnou,cnou));
            }
        }
    }
    if(w[stoplin][stopcol] == 0)
        return 0;
    return 1;
}

int main()
{
    fin >> n >> m;
    for(int i = 1; i <= n; i ++)
    {
        for(int j = 1; j <= m; j ++)
        {
            char c;
            fin >> c;
            if(c == 'D')
            {
                coada.push(make_pair(i,j));
                v[i][j] = 1;
            }
            if(c == 'I')
            {
                startlin = i;
                startcol = j;
            }
            if(c == 'O')
            {
                stoplin = i;
                stopcol = j;
            }
            if(c == '*')
            {
                v[i][j] = -1;
            }
        }
    }

    Lee();

    int st = 1, dr = n * m;
    int ans = 0;

    while(st <= dr)
    {
        int mijloc = (st + dr) / 2;
        int sol = -1;
        sol = parcurgere(mijloc);
        if(sol == 0)
        {
            st = mijloc + 1;
            ans = mijloc;
        }
        else
            dr = mijloc - 1;
    }
    if(ans)
        fout << ans << '\n';
    else
        fout << -1 << '\n';
    return 0;
}