#include <fstream>
#include <queue>
#include <vector>
#include <utility>
#include <cstring>
#define FOR(i,a,b) for(int i = a; i<=b; i++)
#define NMAX 1005
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");

char mat[NMAX][NMAX];
int f[NMAX][NMAX];
bool fp[NMAX][NMAX];
vector<pair<int,int> > drag;
int xfi,yfi,xst,yst;
int dl[5] = {-1,0,1,0};
int dc[5] = {0,1,0,-1};
int sol;
int N,M;
void Citire();
void InitializationFill();
int CautareBinara();
bool Verificare(int x);

int main()
{
    Citire();
    InitializationFill();

 /*   FOR(i,1,N)
    {
        FOR(j,1,M)
            fout<<f[i][j]<<" ";
        fout<<'\n';
    }*/
    fout<<CautareBinara()<<'\n';
    return 0;
}


bool Verificare(int dist)
{
    FOR(i,1,N)
        memset(fp[i],0,sizeof(fp[i]));
    queue<pair<int,int> > Q;
    Q.push(make_pair(xst,yst));
    fp[xst][yst] == 1;

    bool found = false;
    while(!Q.empty())
    {
        int x = Q.front().first;
        int y = Q.front().second;
        Q.pop();

        FOR(j,0,3)
        {
            int nx = x + dl[j];
            int ny = y + dc[j];

            if(fp[nx][ny] == 0 && f[nx][ny]!= -1 && f[nx][ny] - 1 >= dist)
            {
                fp[nx][ny] = 1;
                if(nx == xfi && ny == yfi)
                {
                    return true;
                }
                Q.push(make_pair(nx,ny));
            }
        }
    }
    return fp[xfi][yfi];
}

int CautareBinara()
{
    int st = 0, fi = N+M,mij;
    bool val;
    sol = -NMAX;
    while(fi-st > 1)
    {
        mij = (fi+st)/2;
        val = Verificare(mij);
        if(val == true)
        {
            sol = max(sol,mij);
            st = mij;
        }
        else
        {

            fi = mij;
        }
    }
    if(fi == 2*NMAX || sol == -NMAX || sol == 0)
        return -1;
    return sol;
}

void Citire()
{
    fin>>N>>M;
    FOR(i,1,N)
        FOR(j,1,M)
        {
            fin>>mat[i][j];
            if(mat[i][j] == '*')
                f[i][j] = -1;
            else if(mat[i][j] == 'D')
            {
                f[i][j] = -2;
                drag.push_back(make_pair(i,j));
            }
            else if(mat[i][j] == 'O')
            {

                xfi = i;
                yfi = j;
            }
            else if(mat[i][j] == 'I')
            {

                xst = i;
                yst = j;
            }
        }
}

void InitializationFill()
{

    FOR(i,0,M+1)
        f[0][i] = f[N+1][i] = -1;
    FOR(i,0,N+1)
        f[i][0] = f[i][M+1] = -1;

    queue<pair<int, int> > Q;
    FOR(i,0,(drag.size()-1))
    {
        Q.push(drag[i]);
        f[drag[i].first][drag[i].second] = 1;
    }

    while(!Q.empty())
        {
            int x = Q.front().first;
            int y = Q.front().second;
            Q.pop();

            FOR(j,0,3)
            {
                int nx = x + dl[j];
                int ny = y + dc[j];

                if(f[nx][ny]!= -1 && (f[nx][ny] == 0 || f[nx][ny] > f[x][y] + 1))
                {
                       f[nx][ny] = f[x][y]+1;
                       Q.push(make_pair(nx,ny));
                }
            }

        }

      /*  FOR(k,0,N+1)
    {
        FOR(j,0,M+1)
            fout<<f[k][j]<<" ";
        fout<<'\n';
    }
    fout<<'\n'<<'\n';
    */
}