#include<fstream>
#include<cstring>
#include<queue>
#include<vector>
#define N 1010
#define NM 1000020
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
int dx[]={0,1,-1,0,0};
int dy[]={0,0,0,1,-1};
queue<int> qx,qy,Q;
int dr,st,e[N][N],i,t,dest,d,sol,nod,j,n,m,mij,E[NM],dsol,xi,yi,xf,yf,yc,xc,x,y,c[N][N];
vector<int> v[NM];
int viz[NM];
char ch;
void prec()
{
    while(!qx.empty())
    {
        x=qx.front();y=qy.front();
        qx.pop();qy.pop();
        for(i=1;i<=4;++i)
        {
            xc=x+dx[i];
            yc=y+dy[i];
            if(xc<1||yc<1||xc>n||yc>m||e[xc][yc]||c[xc][yc])
                continue;
            e[xc][yc]=e[x][y]+1;
            qx.push(xc); qy.push(yc);
        }
    }
}
void init()
{
	++t;
	c[xi][yi]=t;
	qx.push(xi);
	qy.push(yi);
	E[t]=e[xi][yi];
	while(!qx.empty())
	{
		x=qx.front();y=qy.front();
		if(c[x][y]==14)
		{
			x++;
			x--;
		}
		qx.pop();qy.pop();
		for(i=1;i<=4;++i)
		{
			xc=x+dx[i];yc=y+dy[i];
			if(xc<1||yc<1||xc>n||yc>m)
				continue;
			if(!c[xc][yc])
			{
			c[xc][yc]=++t;
			if(xc==xf&&yc==yf)
				dest=t;
			E[t]=e[xc][yc];
			qx.push(xc);
			qy.push(yc);
			}
			v[c[x][y]].push_back(c[xc][yc]);
		}
	}
}
int bfs(int mid)
{
	memset(viz,0,t+2);
	Q.push(1);
	viz[1]=1;
    while(!Q.empty())
    {
        nod=Q.front();
		Q.pop();
		if(nod==dest)
		{
			while(!Q.empty())
				Q.pop();
			return 1;
		}
		for(i=0;i<v[nod].size();++i)
		{
			d=v[nod][i];
			if(!viz[d]&&E[d]>=mid)
			{
				Q.push(d);
				viz[d]=1;
			}
		}
	}
    return 0;
}
int main()
{
    f>>n>>m;
    for(i=1;i<=n;++i)
        for(j=1;j<=m;++j)
        {
            f>>ch;
            if(ch=='D')
            {
                qx.push(i);
                qy.push(j);
                c[i][j]=1;
            }
            else
            if(ch=='I')
                xi=i,yi=j;
            else
            if(ch=='O')
                xf=i,yf=j;
            else
            if(ch=='*')
                c[i][j]=1;
        }
    prec();
    st=1;
    dr=min(e[xi][yi],e[xf][yf]);
	init();
    while(st<=dr)
    {
        mij=(st+dr)>>1;
        if(bfs(mij))
        {
            sol=mij;
            st=mij+1;
        }
        else
            dr=mij-1;
    }
    if(!sol)
        g<<"-1";
    else
        g<<sol;
    return 0;
}