#include <bits/stdc++.h>

using namespace std;

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

int n, m, sx, sy, st, dr, mid, fx, fy;
int harta[1005][1005], lee[1005][1005];
char ch;

queue< pair<int, int> > coada;
int x, y, x_next, y_next;

int dx[4] = { -1,  0, 0, 1 };
int dy[4] = {  0, -1, 1, 0 };

void golireDrum()
{
    for( int i = 1; i <= n; i++ )
        for( int j = 1; j <= m; j++ )
            if( lee[i][j] != -1 )
                lee[i][j] = 0;
}

bool OK( int px, int py, int val )
{
    if( px < 1 || py < 1 || px > n || py > m )
        return false;

    if( lee[px][py] != 0 )
        return false;

    if( harta[px][py] < val )
        return false;

    return true;
}

void Lee( int val )
{
    queue< pair<int, int> > c;
    c.push( make_pair( sx, sy ) );
    lee[sx][sy] = 1;

    while( !c.empty() )
    {
        x = c.front().first;
        y = c.front().second;
        c.pop();

        for( int d = 0; d <= 3; d++ )
        {
            x_next = x + dx[d];
            y_next = y + dy[d];

            if( OK( x_next, y_next, val ) )
            {
                lee[x_next][y_next] = lee[x][y] + 1;
                c.push( make_pair(x_next, y_next) );
            }
        }
    }
}

int main(){

    in>>n>>m;
    for( int i = 1; i <= n; i++ )
        for( int j = 1; j <= m; j++ )
        {
            in>>ch;

            switch( ch )
            {
                case '*': harta[i][j] = lee[i][j] = -1; break;
                case 'I': sx = i;
                          sy = j;
                          break;
                case 'D': harta[i][j] =  1;
                          coada.push( make_pair(i, j) );
                          break;
                case 'O': fx = i;
                          fy = j;
                          break;
            }
        }

    while( !coada.empty() )
    {
        x = coada.front().first;
        y = coada.front().second;
        coada.pop();

        for( int d = 0; d <= 3; d++ )
        {
            x_next = x + dx[d];
            y_next = y + dy[d];

            if( x_next >= 1 && y_next >= 1 && x_next <= n && y_next <= m && harta[x_next][y_next] == 0 )
            {
                harta[x_next][y_next] = harta[x][y] + 1;
                coada.push( make_pair(x_next, y_next) );
            }
        }
    }



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

    while( st <= dr )
    {
        mid = (st + dr)/2;

        Lee( mid );

        if( lee[n][m] > 0 )
            st = mid + 1;
        else
            dr = mid - 1;

        golireDrum();
    }

    out<<dr;

    return 0;
}