#include <fstream>
#include <iomanip>
#include <vector>
#include <queue>
using namespace std;

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

const int INF = 0x3f3f3f3f;
const int di[] = { -1, 0, 1, 0 },
          dj[] = { 0, 1, 0, -1 };
int m, n, i1, j1, i2, j2, dmax, iv, jv, i, j;
int d[1001][1001];
char a[1001][1001];
queue<pair< int, int> > Q;

void Read();
void Lee();
bool Ok ( int i, int j );
void Write();
bool Check( int x );
void Solve();

int main()
{
    Read();
    Lee();
    //Write();
    Solve();
    is.close();
    os.close();
    return 0;
}

void Solve()
{
    for ( int i = d[i1][j1]; i >= 1; i--)
        if ( Check(i) == true)
        {
            os << i;
            return;
        }
    os << -1;
}

bool Check( int x )
{
    deque<pair<int, int> > q;
    vector<vector<bool> > ver ( m + 1, vector<bool>( n + 1, false));
    int i = i1, j = j1;
    q.push_back(make_pair(i, j) );
    ver[i1][j1] = true;
    while ( !q.empty() )
    {
        i = q.front().first, j = q.front().second;
        q.pop_front();
        for ( int k = 0; k < 4; k++ )
        {
            iv = i + di[k], jv = j + dj[k];
            if ( Ok(iv, jv ) && ver[iv][jv] == false && d[iv][jv] >= x )
            {
                ver[iv][jv] = true, q.push_back(make_pair(iv, jv));
                if ( iv == i2 && jv == j2 )
                    return true;
            }
        }
    }
    return false;
}

void Lee()
{
        while ( !Q.empty() )
        {
            i = Q.front().first;
            j = Q.front().second;
            Q.pop();
            for ( int k = 0; k < 4; k++ )
            {
                iv = i + di[k], jv = j + dj[k];
                if ( Ok( iv, jv ) && d[iv][jv] == 0 )
                {
                    d[iv][jv] = d[i][j] + 1;
                    dmax = max(dmax, d[iv][jv]);
                    Q.push(make_pair(iv, jv ));
                }
            }
        }
}

bool Ok( int i, int j )
{
    if ( i < 1 || j < 1 || i > m || j > n )
        return false;
    if ( a[i][j] == '*' || a[i][j] == 'D' )
        return false;
    return true;
}

void Read()
{
    is >> m >> n;
    for ( int i = 1; i <= m; i++ )
        for ( int j = 1; j <= n; j++ )
        {
            is >> a[i][j];
            if ( a[i][j] == 'I' )
                i1 = i, j1 = j;
            if ( a[i][j] == 'O' )
                i2 = i, j2 = j;
            if ( a[i][j] == 'D' )
               Q.push(make_pair(i,j));
        }
}

void Write()
{
    for ( int i = 1; i <= m; i++ )
    {
        for ( int j = 1; j <= n; j++ )
                os << d[i][j] << ' ';
        os << '\n';
    }
}