#include<fstream>
#include<deque>
#include<bitset>
#include<cstring>
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
const int dx[]={-1,0,1,0};
const int dy[]={0,1,0,-1};
bitset<1005>viz[1005];
deque<int>qx,qy;
int X,Y;
int v[1005][1005];
void lee()
{
    int x,y,nx,ny;
    while(!qx.empty())
    {
        x=qx.front();
        y=qy.front();
        qx.pop_front();
        qy.pop_front();
        for(int i=0;i<4;i++)
        {
            nx=x+dx[i];
            ny=y+dy[i];
            if(v[nx][ny]==0)
            {
                v[nx][ny]=v[x][y]+1;
                qx.push_back(nx);
                qy.push_back(ny);
            }
        }
    }
}
void solve(int lim, bool &is)
{
    memset(viz,0,sizeof(viz));
    viz[qx.front()][qy.front()]=1;
    int x,y,nx,ny;
    while(!qx.empty())
    {
        x=qx.front();
        y=qy.front();
        qx.pop_front();
        qy.pop_front();
        for(int i=0;i<4;i++)
        {
            nx=x+dx[i];
            ny=y+dy[i];
            if(viz[nx][ny]==0&&v[nx][ny]>lim)
            {
                if(nx==X&&ny==Y)
                {
                    is=true;
                    qx.clear();
                    qy.clear();
                    return;
                }
                viz[nx][ny]=1;
                qx.push_back(nx);
                qy.push_back(ny);
            }
        }
    }
}
int main()
{
    string read;
    int n,m,x,y;
    f>>n>>m;
    for(int i=1;i<=n;i++)
    {
        f>>read;
        read=" "+read;
        for(int j=1;j<=m;j++)
        {
            if(read[j]=='*')
              v[i][j]=-1;
            else
            {
                if(read[j]=='D')
                {
                    v[i][j]=1;
                    qx.push_back(i);
                    qy.push_back(j);
                }
                else
                {
                    if(read[j]=='I')
                    {
                        x=i;
                        y=j;
                    }
                    else if(read[j]=='O')
                    {
                        X=i;
                        Y=j;
                    }
                }
            }
        }
    }
    for(int i=0;i<=n+1;i++)
      v[i][0]=v[i][m+1]=-1;
    for(int j=0;j<=m+1;j++)
      v[0][j]=v[n+1][j]=-1;
    lee();
    int st=0,dr=n*m,mij,ans;
    bool is;
    ans=0;
    while(st<=dr)
    {
        mij=(st+dr)>>1;
        is=false;
        qx.push_back(x);
        qy.push_back(y);
        solve(mij,is);
        if(is==true&&v[x][y]>mij)
        {
            st=mij+1;
            ans=1;
        }
        else
          dr=mij-1;
    }
    if(ans)
      g<<dr;
    else
      g<<-1;
    return 0;
}