# include <fstream>
# include <iostream>
using namespace std;
struct nod {
	int i, j;
	nod *next;};
int a[1003][1003], n, m, d[1003][1003], ist, jst, ifin, jfin, c[1003][1003];
int di[4]={0, 0, 1, -1}, dj[4]={-1, 1, 0, 0};
nod *st, *dr;

void read ()
{
	nod *t;
	st=dr=new nod;
	st->next=NULL;
	ifstream fin ("barbar.in");
	fin>>n>>m;
	char c;
	for (int i=1;i<=n;i++)
		for (int j=1;j<=m;j++)
		{
			fin>>c;
			if (c=='.')	a[i][j]=1;
			else if (c=='*') a[i][j]=-1;
				else if (c=='D')
					{a[i][j]=0;t=new nod;t->i=i;t->j=j;t->next=NULL;dr->next=t;dr=t;}
					else if (c=='I'){a[i][j]=1;ist=i;jst=j;}
						else if (c=='O'){a[i][j]=1;ifin=i;jfin=j;}
		}
	t=st;
	st=st->next;
	delete t;
}
int IN_M(int i, int j)
{
	if (i<=n && i>0 && j<=m && j>0)
		return 1;
	return 0;
}

void distante ()
{
	int i, j, ii, jj, k;
	while (st)
	{
		i=st->i;
		j=st->j;
		for (k=0;k<4;k++)
		{
			ii=i+di[k];
			jj=j+dj[k];
			if (d[ii][jj]==0 && a[ii][jj]==1 && IN_M(ii, jj))
			{
				d[ii][jj]=d[i][j]+1;
				nod *t=new nod;
				t->i=i;
				t->j=j;
				t->next=NULL;
				dr->next=t;
				dr=t;
			}
		}
		nod *q=st;
		st=st->next;
		delete q;
	}
}

void drum ()
{
	int k, i, j, ii, jj;
	nod *t, *st, *dr;
	st=dr=new nod;
	st->i=ist;
	st->j=jst;
	st->next=NULL;
	c[ist][jst]=d[ist][jst];
	while (st)
	{
		i=st->i;
		j=st->j;
		for (k=0;k<4;k++)
		{
			ii=i+di[k];
			jj=j+dj[k];
			if (IN_M(ii, jj) && a[ii][jj]!=-1)
			{
				if (c[ii][jj]==0)
				{
					if (ii!=ifin && jj!=jfin)
						t=new nod;t->i=ii;t->j=jj;t->next=NULL;dr->next=t;dr=t;
					if (d[ii][jj]<c[i][j])c[ii][jj]=d[ii][jj];
					else c[ii][jj]=c[i][j];
				}
				else
					if (c[i][j]>c[ii][jj] && d[ii][jj]>=c[i][j])
						c[ii][jj]=c[i][j];
			}
		}
		t=st;
		st=st->next;
		delete t;
	}
}
	

int main ()
{
	read ();
	distante ();
	drum ();
	ofstream fout ("barbar.out");
	fout<<c[ifin][jfin];
	return 0;
}