#include <bits/stdc++.h>
using namespace std;
ifstream f ("barbar.in");
ofstream g ("barbar.out");
const int nmax=1003;
int i,j,n,m,st,dr,ok,v[nmax][nmax],b[nmax][nmax],xi,yi,xf,yf,xc,yc,xin,yin,mid,okk,dx[]={0,0,1,-1},dy[]={1, -1, 0, 0};
struct usu
{
    int x, y;
}aux;
deque <usu> c;
char ch;
int check(int x, int y)
{
    if(x>n||x<1||y>m||y<1) return 0;
    return 1;
}
int main()
{
    f>>n>>m;
    for(i=1;i<=n;++i)
    {
        for(j=1;j<=m;++j)
        {
            f>>ch;
            if(ch=='*') v[i][j]=-1;
            if(ch=='D')
            {
                aux.x=i;
                aux.y=j;
                c.push_back(aux);
                v[i][j]=1;
            }
            if(ch=='I') xin=i,yin=j;
            if(ch=='O') xf=i,yf=j;
        }
    }
    while(!c.empty())
    {
        aux=c.front();
        xi=aux.x;
        yi=aux.y;
        for(i=0;i<=3;++i)
        {
            xc=xi+dx[i];
            yc=yi+dy[i];
            if(v[xc][yc]==0&&check(xc,yc))
            {
                v[xc][yc]=v[xi][yi]+1;
                aux.x=xc;
                aux.y=yc;
                c.push_back(aux);
            }
        }
        c.pop_front();
    }
    st=1;
    dr=max(n,m);
    while(st<=dr)
    {
        mid=(st+dr)/2;
        c.clear();
        aux.x=xin;
        aux.y=yin;
        if(mid>v[xin][yin])
        {
            dr=mid-1;
            continue;
        }
        b[xin][yin]=mid;
        c.push_back(aux);
        ok=0;
        while(!c.empty()&&ok==0)
        {
            aux=c.front();
            xi=aux.x;
            yi=aux.y;
            for(i=0;i<=3;++i)
            {
                xc=xi+dx[i];
                yc=yi+dy[i];
                if(v[xc][yc]>=mid&&check(xc,yc)&&b[xc][yc]!=mid)
                {
                    b[xc][yc]=mid;
                    aux.x=xc;
                    aux.y=yc;
                    c.push_back(aux);
                    if(xc==xf&&yc==yf) ok=1;
                }
            }
            c.pop_front();
        }
        if(ok==1)
        {
            st=mid+1;
            okk=1;
        }
        else dr=mid-1;
    }
    if(dr-1>=0) g<<dr-1;
    else g<<-1;
    return 0;
}