#include <iostream>
#include <fstream>
#include <vector>
#include <cmath>
#include <cstdio>
#include <queue>

using namespace std;

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


#define NMAX 1010

int n, m;
int a[NMAX][NMAX];
int dx[] = {-1, 0, 0, 1}, dy[] = {0, -1, 1, 0};
pair<int, int> start, finish;
queue<pair<int, int>> Q;

bool test(int k)
{
    if(k > a[start.first][start.second])
        return 0;
    bool viz[NMAX][NMAX] = {0};
    Q.push(start);
    viz[start.first][start.second];
    while(!Q.empty())
    {
        pair<int, int> nod = Q.front();
        if(nod.first == finish.first && nod.second == finish.second)
        {
            while(!Q.empty()) Q.pop();
            return 1;
        }
        Q.pop();
        for(int i = 0 ; i < 4; i++)
        {
            int new_x = nod.first + dx[i];
            int new_y = nod.second + dy[i];
            if(!viz[new_x][new_y] && a[new_x][new_y] >= k)
            {
                viz[new_x][new_y] = 1;
                Q.push(make_pair(new_x, new_y));
            }

        }
    }
    if(viz[finish.first][finish.second])
        return 1;
    return 0;
}

int cauta()
{
    int st = 2, dr = 2000, sol = -1 , mid;
    while(st <= dr)
    {
        int mij = (dr + st ) / 2;
        if(test(mij))
        {
            sol = mij;
            st = mij+1;
        }
        else
            dr = mij - 1;
    }
    return sol;
}

void Lee()
{
    while(!Q.empty())
    {
        int x = Q.front().first;
        int y = Q.front().second;
        Q.pop();
        for(int i = 0 ; i < 4; i++)
        {
            int new_x = x + dx[i];
            int new_y = y + dy[i];
            if(!a[new_x][new_y])
            {
                a[new_x][new_y] = a[x][y] + 1;
                Q.push(make_pair(new_x, new_y));
            }
            else if(a[new_x][new_y] > a[x][y] + 1)
                a[new_x][new_y] = a[x][y] + 1;

        }
    }
}

void bordare()
{
    for(int i = 1; i <= n; i++)
        a[i][0] = a[i][m + 1] = -1;
    for(int j = 1; j <= m; j++)
        a[0][j] = a[n+1][j] = -1;
}

void citire()
{
    fin>>n>>m;
    char s[NMAX];
    fin.get();
    for(int i = 1; i <= n; i++)
    {
        fin.getline(s, NMAX);
        for(int j = 0; j < m; j++)
            switch(s[j])
            {
            case 'I':
                start = make_pair(i, j + 1);
                break;
            case 'D':
                a[i][j + 1] = 1;
                Q.push(make_pair(i, j + 1));
                break;
            case 'O':
                finish = make_pair(i, j + 1);
                break;
            case '*':
                a[i][j+1] = -1;
                break;
            }
    }
}

int main()
{
    citire();
    bordare();
    Lee();
    fout<<cauta() - 1;
    return 0;
}