#include<fstream>
#include<vector>
#include<queue>
#define inf 10000000
using namespace std;
ofstream g("barbar.out");
int n,m,i,j,d[1001][1001],a[1001][1001],xi,yi,xf,yf,st,dr,mij,rez=0;
char x;
int dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
struct coord
{
    int i,j;
};
queue<coord>q;
void lee()
{
    int x,y,xx,yy,i;

    while(!q.empty())
    {
        x=q.front().i;
        y=q.front().j;

        for(i=0;i<4;i++)
        {
        xx=x+dx[i];
        yy=y+dy[i];
        if(d[xx][yy]>d[x][y]+1&&xx<=n&&yy<=m&&xx>0&&yy>0)
           {
            d[xx][yy]=d[x][y]+1;
            q.push((coord){xx,yy});

           }
        }

        q.pop();
    }
}

int lee1(int val)
{
    int x,y,xx,yy,i;
    q.push((coord){xi,yi});
    while(!q.empty())
    {
        x=q.front().i;
        y=q.front().j;
        for(i=0;i<4;++i)
        {
            xx=x+dx[i];
            yy=y+dy[i];
            if(d[xx][yy]>=val&&xx<=n&&yy<=m&&xx>0&&yy>0&&a[xx][yy]!=val&&d[xx][yy]!=-1)
            {
                a[xx][yy]=val;
                q.push((coord){xx,yy});

                if(xx==xf&&yy==yf)
                {
                    while(!q.empty())
                    q.pop();
                    return 1;
                }
            }
        }
        q.pop();
    }
    return 0;
}
int main()
{

    ifstream f("barbar.in");

    f>>n>>m;
    for(i=1;i<=n;++i)
        for(j=1;j<=m;++j)
        {
           f>>x;
           if(x=='.')
           a[i][j]=d[i][j]=inf;
           else
           if(x=='*')
           a[i][j]=d[i][j]=-1;
           else
           if(x=='I')
           {
           xi=i,yi=j;
           d[i][j]=a[i][j]=inf;
           }
           else
           if(x=='O')
           {
               d[i][j]=a[i][j]=inf;
           xf=i,yf=j;
           }
           else
           if(x=='D')
           {
           q.push((coord){i,j});
           d[i][j]=0;
           }
        }

        lee();

        st=1, dr=d[xf][yf];

        while(st<dr)
        {
            mij=(st+dr)/2;
           if(lee1(mij))
           {
           st=mij+1;
           if(mij>rez)
           rez=mij;
           }
           else
           dr=mij-1;

        }
        if(rez)
        g<<rez;
        else
        g<<-1;
    return 0;

}