#include <bits/stdc++.h>
#define oo 2e9
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
char a[1005][1005];
int d[1005][1005];
bool b[1005][1005];
int n, m;
int xs, ys, xf, yf;

int dx[] = {-1, 0, 0, 1};
int dy[] = {0, -1, 1, 0};
queue<pair<int, int>> q;
void Lee()
{
    int i, j, x, y;
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop();
        for (int k = 0; k < 4; k++)
        {
            x = i + dx[k];
            y = j + dy[k];
            if (a[x][y] != '*' && d[x][y] > d[i][j] + 1)
            {
                d[x][y] = d[i][j] + 1;
                q.push({x, y});
            }
        }
    }
}
void Fill(int DisMin)
{
    int i, j, x, y;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
            b[i][j] = 0;
    b[xs][ys] = 1;
    q.push({xs, ys});
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop();
        for (int k = 0; k < 4; k++)
        {
            x = i + dx[k];
            y = j + dy[k];
            if (a[x][y] != '*' && d[x][y] >= DisMin && b[x][y] == 0)
            {
                b[x][y] = 1;
                q.push({x, y});
            }
        }
    }
}
void Rezolvare()
{
    int st, dr, mij, DisMax;
    st = 0; dr = 2e3;
    DisMax = 0;
    while (st <= dr)
    {
        mij = (st + dr) / 2;
        Fill(mij);
        if (b[xf][yf] == 1)
        {
            DisMax = mij;
            st = mij + 1;
        }
        else dr = mij - 1;
    }
    if (DisMax == 0)fout << "-1\n";
    else fout << DisMax << "\n";
}
int main()
{
    int i, j;
    fin >> n >> m;
    for (i = 1; i <= n; i++)
        fin >> (a[i] + 1);

    for (i = 0; i <= n + 1; i++)
        a[i][0] = a[i][m + 1] = '*';
    for (j = 0; j <= m + 1; j++)
        a[0][j] = a[n + 1][j] = '*';

    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
            d[i][j] = oo;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
            if (a[i][j] == 'D')
            {
                q.push({i, j});
                d[i][j] = 0;
            }
            else if (a[i][j] == 'I')
            {
                xs = i; ys = j;
            }
            else if (a[i][j] == 'O')
            {
                xf = i; yf = j;
            }
    Lee();
    for (i = 0; i <= n + 1; i++)
        b[i][0] = b[i][m + 1] = 1;
    for (j = 0; j <= m + 1; j++)
        b[0][j] = b[n + 1][j] = 1;
    Rezolvare();
    return 0;
}