#include <fstream>
#include <deque>
#define K 1002
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int n,m,i,j,iv,jv,st,dr,mid,xs,xf,ys,yf,sol,d[K][K];
char a[K][K],f[K][K];
int di[]={0,1,0,-1};
int dj[]={1,0,-1,0};
deque <pair<int,int> > c;
int verif(int x){///verific daca exista drum cu toate celulele >= x
    if(d[xs][ys]<=x)return 0;
    while(!c.empty())
        c.pop_back();
    for(int i=1;i<=n;i++)
        for(int j=1;j<=m;j++)
            f[i][j]=0;
    c.push_back({xs,ys});
    f[xs][ys]=1;
    while(!c.empty()){
        int i=c.front().first;
        int j=c.front().second;
        c.pop_front();
        for(int dir=0;dir<4;dir++){
            int iv=i+di[dir];
            int jv=j+dj[dir];
            if(!(iv && jv && iv<=n && jv<=m))continue;
            if(a[iv][jv]=='*' || a[iv][jv]=='D')continue;
            if(!f[iv][jv] && d[iv][jv]>x){
                if(iv==xf && jv==yf)return 1;
                c.push_back({iv,jv});
                f[iv][jv]=1;
            }
        }
    }
    return 0;
}
int main(){
    fin>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++){
            fin>>a[i][j];
            if(a[i][j]=='I')
                xs=i, ys=j;
            if(a[i][j]=='O')
                xf=i, yf=j;
            if(a[i][j]=='D'){
                c.push_back({i,j});
                d[i][j] = 1;
            }
        }
    while(!c.empty()){///calculez pt fiecare celula distanta pana la cel mai apropiat dragon
        i=c.front().first;
        j=c.front().second;
        c.pop_front();
        for(int dir=0;dir<4;dir++){
            iv=i+di[dir];
            jv=j+dj[dir];
            if(!(iv && jv && iv<=n && jv<=m))continue;
            if(a[iv][jv]=='*')continue;
            if(d[iv][jv]==0){
                d[iv][jv]=d[i][j]+1;
                c.push_back({iv,jv});
            }
        }
    }
    st=1; dr=2005; sol=-1;
    while(st<=dr){
        mid=(st+dr)/2;
        if(verif(mid))///exista drum cu distantele >= mid,deci caut o sol mai mare
            st=mid+1,sol=mid;
        else dr=mid-1;
    }
    if(sol>0)fout<<sol;
    else fout<<-1;
    return 0;
}