#include <fstream>
#include <queue>

using namespace std;

const int N = 1000;

char a [ N ][ N ];
int dist [ N ][ N ], traseu [ N ][ N ];

int d_lin[4] = { -1, 0, 1, 0 };
int d_col[4] = { 0, 1, 0, -1 };

queue < pair <int, int> > lee;

int main ( ) {
    
    ifstream fin ( "barbar.in" );
    ofstream fout ( "barbar.out" );
    
    int n, m, i, j, lin0 = 0, col0 = 0, linF = 0, colF = 0, max = 0, ok = 0;
    
    fin >> n >> m;
    
    for ( i = 0; i < n; i++ ){
        
        for ( j = 0; j < m; j++ ){
            
            fin >> a [ i ][ j ];
            
            if ( a[ i ][ j ] == 'D' ){
                lee.push ( { i, j } );
                dist [ i ][ j ] = 1;
            }
            
            if ( a[ i ][ j ] == '*' ){
                dist [ i ][ j ] = -1;
            }
        }
    }
    
    while ( lee.size () > 0 ) {
        
        pair <int, int> c = lee.front();
        
        lee.pop();
        
        if ( c.first >= 0 && c.first < n && c.second >= 0 && c.second < m && dist[ c.first ][ c.second ] != -1 ){
            
            for ( int i = 0; i < 4; i++ ) {
                
                int lin1 = c.first + d_lin [ i ];
                int col1 = c.second + d_col [ i ];
                
                if ( lin1 >= 0 && lin1 < n && col1 >= 0 && col1 < m && dist [ lin1 ][ col1 ] == 0 ) {
                    
                    dist [ lin1 ][ col1 ] = dist[ c.first ][ c.second ] + 1;
                    lee.push ( { lin1, col1 } );
                    
                }
            }
        }
    }
    
    for ( i = 0; i < n; i++ ){
        
        for ( j = 0; j < m; j++ ){
            
            if ( a [ i ][ j ] == 'I' ){
                lin0 = i;
                col0 = j;
            }
            
            if ( a [ i ][ j ] == 'O' ){
                linF = i;
                colF = j;
            }
            
            dist [ i ][ j ] -- ;
            
            if ( dist [ i ][ j ] > max )
                max = dist [ i ][ j ];
        }
    }
    
    int st = 0, dr = max + 1, mij;
    
    while ( dr - st > 1 ) {
        
        mij = ( dr + st ) / 2;
        
        lee.push ( { lin0, col0 } );
        traseu[ lin0 ][ col0 ] = 1;
        
        while ( traseu [ linF ][ colF ] == 0 && lee.size ( ) > 0 ) {
            
            pair < int, int > c = lee.front ( );
            lee.pop ( );
            
            for ( int i = 0; i < 4; i++ ) {
                
                int lin1 = c.first + d_lin [ i ];
                int col1 = c.second + d_col [ i ];
                
                if ( lin1 >= 0 && lin1 < n && col1 >= 0 && col1 < m && traseu [ lin1 ][ col1 ] == 0 && dist [ lin1 ][ col1 ] >= mij ) {
                    
                    traseu [ lin1 ][ col1 ] = 1;
                    lee.push ( { lin1, col1 } );
                }
            }
        }
        
        if ( traseu [ linF ][ colF ] == 1 ){
            st = mij;
            ok = 1;
        }
        
        else
            dr = mij;
        
        for ( i = 0; i < n; i++ )
            for ( j = 0; j < m; j++ )
                traseu [ i ][ j ] = 0;
        
        while ( lee.size ( ) > 0 )
            lee.pop ( );
        
    }
    
    if ( ok == 1 )
        fout << st;
    else
        fout << "-1";
    
    return 0;
}