#include <bits/stdc++.h>

using namespace std;

ofstream fout("barbar.out");

int n, m, cmax, xo, yo, xi, yi;
int b[1005][1005], c[1005][1005];
char a[1005][1005];
stack <pair <int, int> > st;

struct Coord
{
    int x, y;
};

queue <Coord> q;

void Citire()
{
    int i, j;
    Coord w;
    ifstream fin("barbar.in");
    fin >> n >> m;
    for(i = 1; i <= n; i++)
        for(j = 1; j <= m; j++)
        {
            fin >> a[i][j];
            if(a[i][j] == 'D')
            {
                w.x = i;
                w.y = j;
                q.push(w);
            }
            if(a[i][j] == 'O')
            {
                xo = i;
                yo = j;
            }
            if(a[i][j] == 'I')
            {
                xi = i;
                yi = j;
            }
        }
    fin.close();
}

void Bordare()
{
    int i;
    for(i = 0; i <= n + 1; i++)
        a[i][0] = a[i][m + 1] = '*';
    for(i = 0; i <= m + 1; i++)
        a[0][i] = a[n + 1][i] = '*';
}

void Lee()
{
    int dx[] = {1, -1, 0,  0};
    int dy[] = {0,  0, 1, -1};
    int i, j, x, y, k;
    Coord w, w1;
    while(!q.empty())
    {
        w = q.front();
        x = w.x;
        y = w.y;
        q.pop();
        for(k = 0; k < 4; k++)
        {
            i = x + dx[k];
            j = y + dy[k];
            if(a[i][j] == '.' &&
               (b[i][j] == 0 || b[i][j] > b[x][y] + 1))
            {
                b[i][j] = b[x][y] + 1;
                w1.x = i;
                w1.y = j;
                q.push(w1);
            }
            else cmax = max(cmax, b[i][j]);
        }
    }
    for(i = 1; i <= n; i++)
        for(j = 1; j <= m ;j++)
            c[i][j] = b[i][j];
    //fout<<cmax;
}

void Fill(int i, int j, int val)
{
    b[i][j] = -1;
    st.push(make_pair(i, j));
    while(!st.empty())
    {
        i = st.top().first;
        j = st.top().second;
        st.pop();
        if(b[i + 1][j] >= val || b[i + 1][j] == -2)
        {
            b[i + 1][j] = -1;
            st.push(make_pair(i + 1, j));
        }
        if(b[i - 1][j] >= val || b[i - 1][j] == -2)
        {
            b[i - 1][j] = -1;
            st.push(make_pair(i - 1, j));
        }
        if(b[i][j + 1] >= val || b[i][j + 1] == -2)
        {
            b[i][j + 1] = -1;
            st.push(make_pair(i, j + 1));
        }
        if(b[i][j - 1] >= val || b[i][j - 1] == -2)
        {
            b[i][j - 1] = -1;
            st.push(make_pair(i, j - 1));
        }
    }
}

void CautBin()
{
    int i, j, mij, st, dr, sol;
    st = 1;
    dr = cmax;
    sol = -1;
    while(st <= dr)
    {
        for(i = 1; i <= n; i++)
            for(j = 1; j <= m; j++)
                b[i][j] = c[i][j];
        b[xo][yo] = -2;
        mij = (st + dr) / 2;
        Fill(xi, yi, mij);
        if(b[xo][yo] == -1)
        {
            sol = mij;
            st = mij + 1;
        }
        else dr = mij - 1;
    }
    fout<<sol;
}

int main()
{
    Citire();
    Bordare();
    Lee();
    CautBin();
    return 0;
}