#include <bits/stdc++.h>

using namespace std;

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

int n,m;
char a[1005][1005];
queue<pair<int,int>>q;
int dl[] = {-1,0,1,0};
int dc[] = {0,1,0,-1};
bool viz[1005][1005];
int d[1005][1005];
bool mat[1005][1005];
int d2[1005][1005];
int fl,fc,il,ic;

void BFS()
{
    for (int i  = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            d[i][j] = 1e9;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (a[i][j] == 'D')
            {
                q.push({i,j});
                d[i][j] = 0;
                viz[i][j] = true;
            }
    while (!q.empty())
    {
        int lin = q.front().first;
        int col = q.front().second;
        q.pop();
        for (int i = 0; i < 4; i++)
        {
            int vecl = lin + dl[i];
            int vecc = col + dc[i];
            if (!viz[vecl][vecc] and vecl >= 1 and vecl <= n and vecc >= 1 and vecc <= m and a[vecl][vecc] != '*')
            {
                d[vecl][vecc] = d[lin][col] + 1;
                q.push({vecl,vecc});
                viz[vecl][vecc] = true;
            }
        }
    }
}

void DFS(int lin,int col)
{
    viz[lin][col] = true;
    for (int i = 0; i < 4; i++)
    {
        int vl = lin + dl[i];
        int vc = col + dc[i];
        if (!viz[vl][vc] and mat[vl][vc] == true)
            DFS(vl,vc);
    }
}

bool ok(int dist)
{
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
        {
            if (d[i][j] >= dist)
                mat[i][j] = true;
            else
                mat[i][j] = false;
            if (a[i][j] == '*' or a[i][j] == 'D')
                mat[i][j] = false;
            viz[i][j] = false;
        }
    DFS(il,ic);
    return viz[fl][fc];
}

int main()
{
    in >> n >> m;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            in >> a[i][j];
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (a[i][j] == 'I')
                il = i,ic = j;
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
            if (a[i][j] == 'O')
                fl = i,fc = j;
    BFS();
    int st = -1,pas = 1 << 15;
    while (pas != 0)
    {
        if (ok(st + pas) == true)
            st += pas;
        pas /= 2;
    }
    out << st;
    return 0;
}