#include <bits/stdc++.h>

using namespace std;

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

int n, m, l0, c0, lf, cf;
char a[1003][1003];
int parlit[1003][1003], d[1003][1003], dragoni[1003][1003];
deque< pair<int, int> > q;
int dx[] = { 0,0,-1,1 };
int dy[] = { -1,1,0,0 };

void Citire()
{
    int i;
    fin >> n >> m;
    fin.get();
    for (i = 1; i <= n; i++)
        fin.getline(a[i] + 1, 1001);
}

void Bordare()
{
    int i, j;
    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] = '*';
}

void Init()
{
    int i, j;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
            parlit[i][j] = d[i][j] = dragoni[i][j] = 2e9;
}

void Arie_Dragoni()
{
    int i, j, x, y, k;
    for (i = 1; i <= n; i++)
        for (j = 1; j <= m; j++)
            if (a[i][j] == 'D')
            {
                q.push_back({i, j});
                dragoni[i][j] = 0;
            }
            else if (a[i][j] == 'I')
            {
                l0 = i;
                c0 = j;
            }
            else if (a[i][j] == 'O')
            {
                lf = i;
                cf = j;
            }
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop_front();
        for (k = 0; k < 4; k++)
        {
            x = i + dx[k];
            y = j + dy[k];
            if (a[x][y] != '*' && dragoni[x][y] > dragoni[i][j] + 1)
            {
                dragoni[x][y] = dragoni[i][j] + 1;
                q.push_back({ x,y });
            }
        }
    }
}

void Lee()
{
    int i, j, x, y, k;
    q.push_back({ l0, c0 });
    d[l0][c0] = 0;
    while (!q.empty())
    {
        i = q.front().first;
        j = q.front().second;
        q.pop_front();
        for (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;
                if(parlit[x][y] == 2e9 || parlit[x][y] < min(parlit[i][j], dragoni[x][y]))
                    parlit[x][y] = min(parlit[i][j], dragoni[x][y]);
                if (q.empty()) q.push_back({ x,y });
                else if (parlit[q.front().first][q.front().second] < parlit[x][y])
                    q.push_front({ x,y });
                else q.push_back({ x,y });
            }
        }
    }
}

int main()
{
    Citire();
    Bordare();
    Init();
    Arie_Dragoni();
    Lee();
    fout << parlit[lf][cf] << "\n";
    fin.close();
    fout.close();
}