#include <bits/stdc++.h>
using namespace std;

char a[1002][1002];
int dist[1002][1002];
int n, m, maxdist = 0, gasit = -1;
int xs, ys, xf, yf;
int dx[] = {1, -1, 0, 0};
int dy[] = {0, 0, -1, 1};
ifstream fin ("barbar.in");
ofstream fout ("barbar.out");
void Read()
{
    fin >> n >> m;
    for (int i = 1; i<=n; i++)
        for (int j = 1; j<=m; j++)
        {
            fin >> a[i][j];
            dist[i][j] = 2e9;
            if (a[i][j] == 'I')
            {
                xs = i; ys = j;
            }
            else if (a[i][j] == 'O')
            {
                xf = i; yf = j;
            }
        }


}



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

void Lee()
{
   queue<pair<int, int>> q;
   for (int i = 1; i<=n;i++)
        for (int j = 1; j<=m; j++)
            if (a[i][j] == 'D')
            {
                q.push({i,j});
                dist[i][j] = 0;
            }
    while (!q.empty())
    {
        int i = q.front().first;
        int j = q.front().second;
        q.pop();
        for (int k = 0; k<4; k++)
        {
            int x = i + dx[k];
            int y = j + dy[k];
            if(a[x][y] != '*' && dist[x][y] > dist[i][j] + 1)
            {
                dist[x][y] = dist[i][j] + 1;
                q.push({x,y});
            }
        }
    }
}

void Fill(int xs, int ys, int mij)
{
    if (dist[xs][ys] < mij) return;
    dist[xs][ys] = -1;
    stack<pair<int,int>> st;
    st.push({xs,ys});
    while(!st.empty())
    {
        int i = st.top().first;
        int j = st.top().second;
        st.pop();
        for (int k = 0; k<4;k++)
        {
            int x = i + dx[k];
            int y = j + dy[k];
            if (a[x][y] != '*' && dist[x][y] >= mij)
            {
                dist[x][y] = -1;
                st.push({x,y});
            }
        }
    }
}

bool Check(int mij)
{
    Fill(xs, ys, mij);
    if (dist[xf][yf] == -1) return true;
    return false;
}

void caut()
{
    int st = 0, dr = maxdist;
    int distcopy[1002][1002];
    for (int i = 1; i<=n; i++)
        for (int j = 1; j <=m; j++)
            distcopy[i][j] = dist[i][j];
    while (st <= dr)
    {
        int mij = (st+dr)/2;
        if (Check(mij))
        {
            gasit = mij;
            st = mij + 1;
        }
        else dr = mij - 1;

        for (int i = 1; i<=n; i++)
            for (int j = 1; j <=m; j++)
                dist[i][j] = distcopy[i][j];
    }

}
void Solve()
{
    Lee();
    for (int i = 1; i<=n;i++)
    {
        for (int j = 1; j<=m; j++)
        {
        if (dist[i][j] != 2e9) maxdist = max(dist[i][j], maxdist);
        }
    }
    caut();
    fout << gasit;
}
int main()
{
    Read();
    Board();
    Solve();




}