#include <fstream>
#include <queue>
using namespace std;
ofstream fout ("barbar.out");
ifstream fin ("barbar.in");
int n,m,i,j,ln,col,rsp,cs,cd,mij;
queue < pair < int , int > > q;
pair < int , int > aux,poz1,poz2;
char s[1024];
int v[1005][1005],dist[1005][1005],ajuns[1005][1005];
int dx[] = { 0 , 0 , 1 , -1 };
int dy[] = { 1 , -1 , 0 , 0 };
bool lee( int nr );
int main()
{
    fin>>n>>m;
    for( i = 1 ; i <= n ; i++ )
    {
        fin.get();
        fin.get( s , 1024 );
        for( j = 0 ; j < m ; j++ )
        {
            if( s[ j ] == '*' )
                v[ i ][ j + 1 ] = -1;
            if( s[ j ] == 'D' )
            {
                v[ i ][ j + 1 ] = -1;
                q.push( { i , j + 1 } );
            }
            if( s[ j ] == 'I' )
                poz1 = { i , j + 1 };
            if( s[ j ] == 'O' )
                poz2 = { i , j + 1 };
        }
    }
    while( q.size() )
    {
        aux = q.front();
        q.pop();
        for( i = 0 ; i < 4 ; i++ )
        {
            ln = aux.first + dx[ i ];
            col = aux.second + dy[ i ];
            if( ln < 1 || col < 1 || ln > n || col > m )
                continue;
            if( v[ ln ][ col ] == 0 && dist[ ln ][ col ] == 0 )
            {
                dist[ ln ][ col ] = dist[ aux.first ][ aux.second ] + 1;
                q.push( { ln , col } );
            }
        }
    }
    cs = 1;
    cd = 1e3;
    rsp = -1;
    while( cs <= cd )
    {
        mij = ( cs + cd ) >> 1;
        if( lee( mij ) )
            cs = mij + 1;
        else
            cd = mij - 1;
    }
    fout<<rsp;
}
bool lee( int nr )
{
    if( nr > dist[ poz1.first ][ poz1.second ] )
        return 0;
    for( i = 1 ; i <= n ; i++ )
        for( j = 1 ; j <= m ; j++ )
            ajuns[ i ][ j ] = 0;
    q.push( poz1 );
    ajuns[ poz1.first ][ poz1.second ] = 1;
    while( q.size() )
    {
        aux = q.front();
        q.pop();
        for( i = 0 ; i < 4 ; i++ )
        {
            ln = aux.first + dx[ i ];
            col = aux.second + dy[ i ];
            if( ln < 1 || col < 1 || ln > n || col > m )
                continue;
            if( v[ ln ][ col ] == 0 && dist[ ln ][ col ] >= nr && ajuns[ ln ][ col ] == 0 )
            {
                ajuns[ ln ][ col ] = 1;
                q.push( { ln , col } );
            }
        }
    }
    if( ajuns[ poz2.first ][ poz2.second ] == 1 )
    {
        rsp = nr;
        return 1;
    }
    return 0;
}