#include <bits/stdc++.h>
#define f first
#define s second
using namespace std ;
const short NR = 1002 ;
ifstream in ("barbar.in") ;
ofstream out ("barbar.out") ;
queue < pair < short , short > > q ;
short n , m , bi , bj , ei , ej ;
short di [ 4 ] = { -1 , 0 , 1 , 0 } ;
short dj [ 4 ] = { 0 , 1 , 0 , -1 } ;
struct element  {
    int tip , val = -1 ;
}a [ NR ][ NR ];

bool ok ( const short i , const short j )   {
    return i && j && i <= n && j <= m ;
}

void bfs () {
    short d , newi , newj ;
    while ( !q.empty() )    {

        pair < short , short > nod = q.front() ;
        q.pop() ;
        for ( d = 0 ; d < 4 ; ++ d )    {
            newi = nod.f + di [ d ] ;
            newj = nod.s + dj [ d ] ;

            if ( ok ( newi , newj ) && a [ newi ][ newj ].tip == 1 && ( a [ newi ][ newj ].val == -1 || ( a [ newi ][ newj ].val > a [ nod.f ][ nod.s ].val + 1 ) ) )   {

                a [ newi ][ newj ].val = a [ nod.f ][ nod.s ].val + 1 ;
                q.push ( { newi , newj } ) ;
            }
        }
    }
}

bool test ( short k )
{
    if ( k > a [ bi ][ bj ].val ) return 0 ;
     short d , newi , newj ;
     bool viz [ NR ][ NR ] = {0}  ;
    q.push( { bi , bj } ) ;
    viz [ bi ][ bj ] = 1 ;
    while ( !q.empty() )    {
        pair < short , short > nod = q.front() ;
        if ( nod.f == ei && nod.s == ej )   {
            while ( !q.empty() )    q.pop() ;
            return 1 ;
        }
        q.pop() ;
        for ( d = 0 ; d < 4 ; ++ d )    {
            newi = nod.f + di [ d ] ;
            newj = nod.s + dj [ d ] ;

            if ( ok ( newi , newj ) && a [ newi ][ newj ].tip == 1 && a [ newi ][ newj ].val != -1 && a [ newi ][ newj ].val >= k && !viz [ newi ][ newj ] )   {

                viz [ newi ][ newj ] = 1 ;
                q.push ( { newi , newj } ) ;
            }
        }
    }
    return 0 ;
}

short bs ()
{
   short st = 1 , dr = 2000 , sol = -1 , mid ;
   while ( st <= dr )   {
    mid = ( st + dr ) >> 1 ;
        if ( test( mid ) )  {
            sol = mid ;
            st = mid + 1 ;
        }
        else dr = mid - 1 ;
   }
   return sol ;
}

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

        char c ;
        in >> c ;
        if ( c == '*' ) a [ i ][ j ].tip = 0 ;
        if ( c == '.' ) a [ i ][ j ].tip = 1 ;
        if ( c == 'D' ) a [ i ][ j ].tip = 2 , q.push ( { i , j } ) , a [ i ][ j ].val = 0 ;
        if ( c == 'I' ) bi = i , bj = j , a [ i ][ j ].tip = 1 ;
        if ( c == 'O' ) ei = i , ej = j , a [ i ][ j ].tip = 1 ;
    }
    bfs() ;
    out << bs() ;
}