#include <stdio.h>
#include <string.h>

#define nmax 1000
#define NIL -1
#define coada_size 1<<12
#define mask ( (1<<12)-1 )

int v[ nmax+2 ][ nmax+2 ];
char drum[nmax+2][nmax+2];
int coada[ coada_size ][2];
int poz_coada;
char dlin[4] = { -1, 0, 1, 0 };
char dcol[4] = { 0, 1, 0, -1 };
int n, m, lstart, cstart, lstop, cstop;

int mini( int a, int b ){
    return ( ( a<=b ) ? a : b );
}

void bordare(){
    int i;
    for( i=0; i<=n+1; i++ )
        v[i][0] = v[i][m+1] = NIL;
    for( i=0; i<=m+1; i++ )
        v[0][i] = v[n+1][i] = NIL;
}

void lee(){
    int poz_start, i;
    poz_start = 0;
    while( poz_start!=poz_coada ){
        for( i=0; i<4; i++ ){
            if( v[ coada[poz_start][0] + dlin[i] ][ coada[poz_start][1] + dcol[i] ] == 0 ){///daca elementul nu a fost adaugat in coada
                v[ coada[poz_start][0] + dlin[i] ][ coada[poz_start][1] + dcol[i] ] = v[ coada[poz_start][0] ][ coada[poz_start][1] ] + 1;
                coada[poz_coada][0] = coada[poz_start][0] + dlin[i];
                coada[poz_coada][1] = coada[poz_start][1] + dcol[i];
                poz_coada = ( poz_coada + 1 ) & mask;
            }
        }
        poz_start = ( poz_start + 1 ) & mask;
    }
}

void initializare(){
    int i;
    for( i=0; i<=n+1; i++ )
        memset( drum[i], 0, sizeof(drum[i]) );
}

int caut_drum( int val_max ){
    initializare();
    int poz_start, i, ans;
    poz_start = 0;
    coada[poz_start][0] = lstart;
    coada[poz_start][1] = cstart;
    drum[lstart][cstart] = 1;
    ans = 0;
    poz_coada = 1;
    while( poz_start!=poz_coada && ans==0 ){
        for( i=0; i<4; i++ ){
            if( drum[ coada[poz_start][0] + dlin[i] ][ coada[poz_start][1] + dcol[i] ] == 0 && ( v[ coada[poz_start][0] + dlin[i] ][ coada[poz_start][1] + dcol[i] ] - 1 ) >= val_max ){
                drum[ coada[poz_start][0] + dlin[i] ][ coada[poz_start][1] + dcol[i] ] = 1;
                coada[poz_coada][0] = coada[poz_start][0] + dlin[i];
                coada[poz_coada][1] = coada[poz_start][1] + dcol[i];
                if( coada[poz_coada][0]==lstop && coada[poz_coada][1]==cstop )
                    ans = 1;
                poz_coada = ( poz_coada + 1 ) & mask;
            }
        }
        poz_start = ( poz_start + 1 ) & mask;
    }
    return ans;
}

int cautbin( int start, int stop ){
    int pivot;
    while( stop-start > 1){
        pivot = (start + stop)>>1;
        if( caut_drum( pivot )==1 )
            start = pivot;
        else
            stop = pivot;
    }
    return start==0 ? NIL : start;
}

int main()
{
    int i, j;
    char ch;
    FILE *fin, *fout;
    fin = fopen( "barbar.in", "r" );
    fscanf( fin, "%d%d\n", &n, &m );
    for( i=1; i<=n; i++ ){
        for( j=1; j<=m; j++ ){
            ch = fgetc( fin );
            if( ch=='*' )
                v[i][j] = NIL;
            else if( ch=='D' ){///adaugam dragonul in coada
                coada[poz_coada][0] = i;
                coada[poz_coada][1] = j;
                poz_coada++;
                v[i][j] = 1;
            }
            else if( ch=='I' ){
                lstart = i;
                cstart = j;
            }
            else if( ch=='O' ){
                lstop = i;
                cstop = j;
            }
        }
        fgetc( fin );
    }
    fclose( fin );
    bordare( n, m );
    ///alcatuim matricea cu dist minim de la un pct la un dragon
    lee();
    ///cautam binar valoarea minima pt care ajunge la rezultat
    fout = fopen( "barbar.out", "w" );
   // fprintf( fout, "%d\n", cautbin( 0, mini( v[lstart][cstart], v[lstop][cstop] ) ) );
   fprintf( "-1", fout );
    fclose( fout );
    return 0;
}