#include <bits/stdc++.h>

using namespace std;
/***********************************************/
const int nmax=2000;
int r,c,xi,xf,yi,yf;
char ch;
int val[nmax][nmax],d[nmax][nmax],a[nmax][nmax];
int xDir[]= {0,1,0,-1};
int yDir[]= {-1,0,1,0};
int rasp=INT_MAX;
queue <pair<int, int> > q;
/***********************************************/
ifstream f("barbar.in");
ofstream g("barbar.out");
/***********************************************/
///------------------------------------------------------------
inline void readInput()
{
    f>>r>>c;
    for(int i=1; i<=r; i++)
    {
        for(int j=1; j<=c; j++)
        {
            f>>ch;
            if(ch=='*') a[i][j]=-1;
             if(ch=='I')
            {
                xi=i;
                yi=j;
            }
            else if(ch=='O')
            {
                xf=i;
                yf=j;
            }
           else if(ch=='D') q.push({i,j});
        }
    }
}
///------------------------------------------------------------
bool IsOnMatrix(int x, int y)
{
    if(x<1 || y<1 || x>r || y>c) return 0;
    if(a[x][y]==-1) return 0;
    return 1;
}
///------------------------------------------------------------
void LeeDragoni()
{
    while(!q.empty())
    {
        int xx=q.front().first;
        int yy=q.front().second;
        q.pop();
        for(int i=0; i<4; i++)
        {
            int lin= xx+xDir[i];
            int col=yy+yDir[i];

            if(IsOnMatrix(lin,col)&& (val[lin][col]>val[xx][yy]+1 || val[lin][col]==0))
            {
                val[lin][col]=val[xx][yy]+1;
                q.push({lin,col});
            }
        }
    }

}
///---------------------------------------------------------------
int verif(int dist)

{

    while(!q.empty())

        q.pop();



    for(int i=1; i<=r; i++)

        for(int j=1; j<=c; j++)

            d[i][j] = 0;



    d[xi][yi] = 1;

    if(val[xi][yi]>=dist) q.push(make_pair(xi, yi));

    else return 0;



    while(!q.empty())

    {

        int ipos = q.front().first;

        int jpos = q.front().second;

        q.pop();

        for(int i=0; i<4; i++)

        {

            int lin = ipos + xDir[i];

            int col = jpos + yDir[i];

            if(IsOnMatrix(lin,col) && val[lin][col]>=dist && (d[lin][col]>d[ipos][jpos]+1 || d[lin][col] == 0))

            {

                if(lin == xf && col == yf) return 1;

                d[lin][col] = d[ipos][jpos] + 1;

                q.push(make_pair(lin,col));

            }

        }

    }

    return 0;

}
///------------------------------------------------------------
void CautareBinara(int st, int dr)
{
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(verif(mij)==1)
        {
            rasp=mij;
            st=mij+1;
        }
        else dr=mij-1;
    }
}
///------------------------------------------------------------
inline void Solution()
{
    CautareBinara(0,r*c);
    if(rasp==INT_MAX) g<<"-1";
    else g<<rasp;
}
///------------------------------------------------------------
int main()
{
    readInput();
    LeeDragoni();
    Solution();
    return 0;
}