#include <bits/stdc++.h>

using namespace std;

ifstream fin  ("barbar.in");
ofstream fout ("barbar.out");

const int INF = (1<<30);
const int MAXN = 1005;

vector <pair <int, int>> dragons;
int closestDragon[MAXN][MAXN], walk[MAXN][MAXN];
char mat[MAXN][MAXN]; string row;
int n, m, sol;

void debug(int test[MAXN][MAXN]){
    for(int i=1; i<=n; i++, cout<<"\n")
        for(int j=1; j<=m; j++, cout<<" ")
            if(mat[i][j] == '*')
                cout<<"*";
            else
                cout<<test[i][j];
}

struct End{
    int ii;
    int jj;
}in, out;

struct cell{
    int ii;
    int jj;
    int dd;
}aux, nod;
int di[] = {+1, -1,  0,  0};
int dj[] = { 0,  0, +1, -1};

void set_dist_from_dragons(){
    queue <cell> q;
    for(int i=0; i<dragons.size(); i++){

        aux = {dragons[i].first, dragons[i].second, 0};

        q.push(aux);

        closestDragon[aux.ii][aux.jj] = 0;
    }

    while(!q.empty()){
        nod = q.front();
        q.pop();

        if(nod.dd != closestDragon[nod.ii][nod.jj])
            continue;

        for(int dir=0; dir < 4; dir++){
            int newi = nod.ii + di[dir];
            int newj = nod.jj + dj[dir];

            if(1 <= newi && newi <= n && 1 <= newj && newj <= m)
                if(mat[newi][newj] != '*')
                    if(closestDragon[newi][newj] == INF){

                        closestDragon[newi][newj] = nod.dd + 1;

                        q.push({newi, newj, nod.dd+1});
                    }
        }
    }
}

void _fill(int i, int j){
    walk[i][j] = 1;
    for(int dir=0; dir < 4; dir++){
        int newi = i + di[dir];
        int newj = j + dj[dir];

        if(1 <= newi && newi <= n && 1 <= newj && newj <= m)
            if(walk[newi][newj] == 0)
                _fill(newi, newj);
    }
}

int main (){
    fin>>n>>m;
    for(int i=1; i<=n; i++){
        fin>>row;
        for(int j=0; j<m; j++){
            mat[i][j+1] = row[j];
            closestDragon[i][j+1] = INF;
        }
    }


    int color;
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++){
            if(mat[i][j] == 'D')
                dragons.push_back({i, j});

            if(mat[i][j] == 'I'){
                in.ii=i;
                in.jj=j;
            }
            if(mat[i][j] == 'O'){
                out.ii=i;
                out.jj=j;
            }
        }
    set_dist_from_dragons(); //debug(closestDragon);

    int md, st=-1, dr=closestDragon[in.ii][in.jj] + 1;
    while(st <= dr){
        md=(dr-st)/2+st;

        for(int i=1; i<=n; i++)
            for(int j=1; j<=m; j++)
                if(mat[i][j] == '*' || closestDragon[i][j] < md)
                    walk[i][j] = -1;
                else
                    walk[i][j] = 0;

        if(walk[in .ii][in .jj] == 0)
            _fill(in.ii, in.jj);

        if(walk[out.ii][out.jj] == 1)
            st=md+1;
        else
            dr=md-1;
    }
    fout<<(st == -1 ? -1 : dr);
    return 0;
}