#include <bits/stdc++.h>
//#pragma GCC optimize("O3")
#define test " test "
#define ll long long
#define pii pair<int, int>
#define FASTIO   \
    cin.tie(0);  \
    cout.tie(0); \
    ios_base::sync_with_stdio(0);
#define FILES                      \
    freopen("barbar.in", "r", stdin); \
    freopen("barbar.out", "w", stdout);
#define testcase             \
    int T;    \
    cin >> T; \
    while (T--)
#define vec vector<int>
using namespace std;

char c[1001][1001];
vector<pii> D;
pii start, finish;
int n, m, dx[] = {0, -1, 0, 1}, dy[] = {-1, 0, 1, 0};
vector<vector<int>> alt;

void drag()
{
    queue <pii> q;
    for(auto i : D)
        q.push(i), alt[i.first][i.second] = 1;
    while(!q.empty())
    {
        int x = q.front().first, y = q.front().second;
        q.pop();
        for(int i = 0; i < 4; i++)
            if(x + dx[i] > 0 && x + dx[i] <= n && y + dy[i] > 0 && y + dy[i] <= m)
                if(!alt[x + dx[i]][y + dy[i]])
                {
                    alt[x + dx[i]][y + dy[i]] = alt[x][y] + 1;
                    q.push({x + dx[i], y + dy[i]});
                }
    }
}

bool lee(int mid)
{
    vector<vector<bool>> idk;
    idk.resize(n + 1, vector<bool>(m + 1));
    queue <pii> q;
    q.push(start);
    idk[start.first][start.second] = 1;
    while(!q.empty())
    {
        int x = q.front().first, y = q.front().second;
        q.pop();
        for(int i = 0; i < 4; i++)
            if(x + dx[i] > 0 && x + dx[i] <= n && y + dy[i] > 0 && y + dy[i] <= m)
            {
                if(!idk[x + dx[i]][y + dy[i]] && alt[x + dx[i]][y + dy[i]] > mid && c[x + dx[i]][y + dy[i]] != '*')
                {
                    idk[x + dx[i]][y + dy[i]] = 1;
                    if(make_pair(x + dx[i], y + dy[i]) == finish)
                        return 1;
                    else
                        q.push({x + dx[i], y + dy[i]});
                }
            }
    }
    return 0;
}

signed main()
{
    FASTIO FILES
    cin >> n >> m;
    alt.resize(n + 1, vector<int>(m + 1));
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
        {
            cin >> c[i][j];
            if(c[i][j] == 'D')
                D.push_back({i, j});
            else if(c[i][j] == 'I')
                start = {i, j};
            else if(c[i][j] == 'O')
                finish = {i, j};

        }

    int mn = INT_MAX;
    for(auto i : D)
        mn = min(mn, min(abs(i.first - start.first) + abs(i.second - start.second), abs(i.first - finish.first) + abs(i.second - finish.second)));
    drag();
    int l = 0, r = mn + 1;
    while(l < r - 1)
    {
        int mid = (l + r) / 2;
        if(lee(mid))
            l = mid;
        else
            r = mid;
    }
    if(lee(l))
        cout << l;
    else
        cout << -1;
    return 0;
}