#include <fstream>
#include <queue>
using namespace std;

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

int h[1002][1002];
int a[1001][1001];

queue <int> ql, qc;

int dl[4] = {-1, 0, 1, 0};
int dc[4] = {0, 1, 0, -1};

void fill()
{
    int la, ca, lv, cv, i;
    while (ql.empty() == 0)
    {
        la = ql.front();
        ca = qc.front();
        ql.pop();
        qc.pop();
        for (i = 0; i<4; i++)
        {
            lv = la + dl[i];
            cv = ca + dc[i];
            if (h[lv][cv] == 0 || h[la][ca] + 1 < h[lv][cv])
            {
                h[lv][cv] = h[la][ca] + 1;
                ql.push(lv);
                qc.push(cv);
            }
        }
    }
}

inline int minf(int a, int b)
{
    if (a<b)
        return a;
    return b;
}

int lee(int ls, int cs, int lf, int cf)
{
    int la, ca, lv, cv, i, v;
    a[ls][cs] = h[ls][cs];
    ql.push(ls);
    qc.push(cs);
    while (ql.empty() == 0)
    {
        la = ql.front();
        ca = qc.front();
        ql.pop();
        qc.pop();
        for (i = 0; i<4; i++)
        {
            lv = la + dl[i];
            cv = ca + dc[i];
            if (h[lv][cv] != -1)
            {
                v = minf(a[la][ca], h[lv][cv]);
                if (v > a[lv][cv])
                {
                    a[lv][cv] = v;
                    ql.push(lv);
                    qc.push(cv);
                }
            }
        }
    }
    return a[lf][cf]-1;
}

int main()
{
    int n, m, i, j;
    int ls, cs, lf, cf;
    char buff[1001];
    fin >> n >> m;
    for (i = 1; i<=n; i++)
    {
        fin >> buff;
        for (j = 0; j<m; j++)
        {
            if (buff[j] == '*')
                h[i][j+1] = -1;
            else if (buff[j] == 'I')
            {
                ls = i;
                cs = j+1;
            }
            else if (buff[j] == 'O')
            {
                lf = i;
                cf = j+1;
            }
            else if (buff[j] == 'D')
            {
                ql.push(i);
                qc.push(j+1);
                h[i][j+1] = 1;
            }
        }
    }
    for (i = 0; i<=n+1; i++)
        h[i][0] = h[i][m+1] = -1;
    for (i = 0; i<=m+1; i++)
        h[0][i] = h[n+1][i] = -1;
    fill();
    fout << lee(ls, cs, lf, cf);
    return 0;
}