#include<iostream>
#include<fstream>
#include<queue>
#include<iomanip>
#define MAX 1010 //limite
using namespace std;
fstream fin("barbar.in",ios::in),fout("barbar.out",ios::out);
int di[]={-1,0,1,0},dj[]={0,1,0,-1},x[MAX][MAX],ap[MAX][MAX];//vectori de directii,matricea de distante,matrice pt bifat dfs
int si,sj,fi,fj,r,c,ok,mij; //start,final,limite
queue <pair<int,pair<int,int>> > q;
bool into(int i,int j)
{
    return (0<i && 0<j && i<=r && j<=c);
}
void bfs()
{
    int i,j,k,cost,a,b;
    while(!q.empty())
    {
        i=q.front().first;
        j=q.front().second.first;
        cost=q.front().second.second;
        for(k=0;k<4;k++)
        {
            a=i+di[k]; b=j+dj[k];
            if(x[a][b]==0 || x[a][b]>cost+1)
            {
                if(into(a,b)==1)
                {
                    x[a][b]=cost+1;
                    q.push(make_pair(a,make_pair(b,cost+1)));
                }
            }
        }
        q.pop();
    }
}
void dfs(int i,int j,int minim)
{
    if(ok==1) return;
    if(i==fi && j==fj && minim>=mij) ok=1;
    int a,b,k;
    ap[i][j]=1;
    for(k=0;k<4;k++)
    {
        a=i+di[k];b=j+dj[k];
        if(ap[a][b]==0 && into(a,b)==1)
        {
            if(mij<=x[a][b]) dfs(a,b,min(minim,x[a][b]));
        }
    }
    ap[i][j]=0;
}
int main()
{
    int i,j,k,a,b,pre,act,start,stop;
    char w;
    fin>>r>>c;
    for(i=1;i<=r;i++)
    {
        for(j=1;j<=c;j++)
        {
            fin>>w;
            if(w=='D')
            {
                x[i][j]=-1;
                q.push(make_pair(i,make_pair(j,0)));
            }
            if(w=='*') x[i][j]=-2;
            if(w=='I') si=i,sj=j;
            if(w=='O') fi=i,fj=j;
        }
    }
    bfs();
    start=1;
    stop=min(x[si][sj],x[fi][fj]);
    while(start<stop)
    {
        mij=(start+stop+1)/2;
        ok=0;
        dfs(si,sj,x[si][sj]);
        if(ok==0)
            stop=mij-1;
        else
            start=mij;
    }
    fout<<start;
    return 0;
}