#include <bits/stdc++.h>

using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int nmax  = 1005;
const int INF = 1e9;
int n, m, dp[nmax][nmax][2], x, y, xx, yy;
queue < pair < int, int > > C;
int di[4] = {1, -1, 0, 0};
int dj[4] = {0, 0, 1, -1};
char matrix[nmax][nmax];

void read()
{
    fin >> n >> m;
    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= m; ++j)
        {
            fin >> matrix[i][j];
            dp[i][j][0] = INF;
            if(matrix[i][j] == 'D')
            {
                dp[i][j][0] = 0;
                C.push({i, j});
            }
            if(matrix[i][j] == 'I')
            {
                x = i;
                y = j;
            }
            if(matrix[i][j] == 'O')
            {
                xx = i;
                yy = j;
            }
        }
}

bool ok(int i, int j)
{
    return i >= 1 && j >= 1 && i <= n && j <= m && matrix[i][j] != '*';
}
bool bfs(int mid)
{
    for(int i = 1; i <= n; ++i)
        for(int j = 1; j <= m; ++j)
            dp[i][j][1] = INF;
    if(dp[x][y][0] < mid)
        return false;
    dp[x][y][1] = 0;
    C.push({x, y});
    while(!C.empty())
    {
        int i = C.front().first;
        int j = C.front().second;
        C.pop();
        for(int d = 0; d < 4; d++)
        {
            int ii = i + di[d];
            int jj = j + dj[d];
            if(ok(ii, jj) && dp[ii][jj][1] == INF && dp[ii][jj][0] >= mid)
            {
                dp[ii][jj][1] = dp[i][j][1] + 1;
                C.push({ii, jj});
            }
        }
    }
    if(dp[xx][yy][1] == INF)
        return false;
    return true;
}
void solve()
{
    while(!C.empty())
    {
        int i = C.front().first;
        int j = C.front().second;
        C.pop();
        for(int d = 0; d < 4; d++)
        {
            int ii =  i + di[d];
            int jj = j + dj[d];
            if(dp[ii][jj][0] > dp[i][j][0] && ok(ii, jj))
            {
                dp[ii][jj][0] = dp[i][j][0] + 1;
                C.push({ii, jj});
            }
        }
    }
    int st = 1, dr = n*m, sol = -1;
    while(st <= dr)
    {
        int mid = (st + dr) / 2;
        if(bfs(mid))
        {
            sol = mid;
            st = mid + 1;
        }
        else
            dr = mid - 1;
    }
    fout << sol;
}
int main()
{
    read();
    solve();
    return 0;
}