#include <fstream>
#include <queue>

using namespace std;

ifstream cin("barbar.in");
ofstream cout("barbar.out");

bool a[1005][1005];
int d[1005][1005], r, c;
int di[4]={-1, 1, 0, 0},
    dj[4]={0, 0, -1, 1};
//0-Up, 1-Down, 2-Left, 3-Right

struct cell
{
    int i, j;
}in, out;
queue<cell> q;

void LEED()
{
    if(q.empty())
        return;
    int s=q.size();
    while(s--)
    {
        cell c=q.front();
        q.pop();
        for(int k=0;k<4;k++)
        {
            if(d[c.i+di[k]][c.j+dj[k]]==-1)
            {
                d[c.i+di[k]][c.j+dj[k]]=d[c.i][c.j]+1;
                q.push({c.i+di[k], c.j+dj[k]});
            }
            else if(d[c.i+di[k]][c.j+dj[k]]!=-2)
                d[c.i+di[k]][c.j+dj[k]]=min(d[c.i+di[k]][c.j+dj[k]], d[c.i][c.j]+1);
        }
    }
    LEED();
}

bool LEEN(int dmin)
{
    if(q.empty())
        return 0;
    int s=q.size();
    while(s--)
    {
        cell c=q.front();
        q.pop();
        for(int k=0;k<4;k++)
            if(d[c.i+di[k]][c.j+dj[k]]>=dmin && a[c.i+di[k]][c.j+dj[k]]==0)
            {
                if(c.i+di[k]==out.i && c.j+dj[k]==out.j)
                    return 1;
                a[c.i+di[k]][c.j+dj[k]]=1;
                q.push({c.i+di[k], c.j+dj[k]});
            }
    }
    return LEEN(dmin);
}

void reset()
{
    while(!q.empty())
        q.pop();
    q.push(in);
    for(int i=1;i<=r;i++)
        for(int j=1;j<=c;j++)
            a[i][j]=0;
    a[in.i][in.j]=1;
}

int caut_bin()
{
    int r=0, pas=(1<<9);
    while(pas)
    {
        reset();
        if(d[in.i][in.j]>=r+pas)
            if(LEEN(r+pas))
                r+=pas;
        pas/=2;
    }
    if(r==0)
        return -1;
    return r;
}

void mark()
{
    for(int i=1;i<=r;i++)
        d[i][0]=d[i][c+1]=-2;
    for(int i=1;i<=c;i++)
        d[0][i]=d[r+1][i]=-2;
}

int main()
{
    char ch;
    cin>>r>>c;
    for(int i=1;i<=r;i++)
        for(int j=1;j<=c;j++)
        {
            d[i][j]=-1;
            cin>>ch;
            if(ch=='*')
                d[i][j]=-2;
            else if(ch=='I')
                in={i, j};
            else if(ch=='O')
                out={i, j};
            else if(ch=='D')
            {
                q.push({i, j});
                d[i][j]=0;
            }
        }
    LEED();
    mark();
    cout<<caut_bin();
    return 0;
}