#include <fstream>
#define INF 1000000000
#define K 1002
#include <deque>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int n,m,i,j,iv,jv,xf,xs,yf,ys,st,dr,mid,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
    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});
   while(!c.empty()){
        i=c.front().first;
        j=c.front().second;
        if(i==xf && j==yf)return 1;
        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(!f[iv][jv] && d[iv][jv]>=x){
                f[iv][jv]=1;
                c.push_back({iv,jv});
            }
        }
   }
   return 0;
}
int main(){
    fin>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++){
            fin>>a[i][j];
            d[i][j]=INF;
            if(a[i][j]=='I')
                xs=i,ys=j;
            if(a[i][j]=='O')
                xf=i,yf=j;
            if(a[i][j]=='D'){
                d[i][j]=0;
                c.push_back({i,j});
            }
        }
    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]==INF){
                d[iv][jv]=1+d[i][j];
                c.push_back({iv,jv});
            }
        }
    }
    st=d[xs][ys]; dr=2000;
    while(st<=dr){
        mid=(st+dr)/2;
        if(verif(mid)) ///exista drum cu distantele >= mid,deci caut o sol mai mare
            st=mid+1;
        else dr=mid-1;
    }
    fout<<dr;
    return 0;
}