#include <fstream>   
#include <string.h>   
#define MAX 1105   
using namespace std;   
  
ifstream fin ("barbar.in");   
ofstream fout ("barbar.out");   
  
const int x[4]={-1,0,0,1};   
const int y[4]={0,-1,1,0};   
  
int a[MAX][MAX],n,m,xi,xf,yf,yi,ii[3000001],jj[3000001],numar,ok=0,minim,b[MAX][MAX];   
  
void citire()   
{   
    char s[1010];   
    fin>>n>>m;   
       fin.getline(s,1030);   
    for (int i=1;i<=n;i++)   
    {   
    fin.getline(s,1010);   
    for (int j=0;j<=m;j++)   
        if (s[j]=='*')   
           a[i][j+1]=-1;   
        else  
           if (s[j]=='D')   
           {   
         ii[numar]=i;   
         jj[numar]=j+1;   
             a[i][j+1]=1;   
         numar++;   
           }   
           else  
         if (s[j]=='I')   
         {   
            xi=i;   
            yi=j+1;   
         }   
         else  
           if (s[j]=='O')   
           {   
              xf=i;   
              yf=j+1;   
           }   
    }   
}   
  
int min (int a,int b)   
{   
   if (a<b)   
      return a;   
   return b;   
}   
  
void lee ()   
{   
    int nr=numar;   
    for (int i=0;i<nr;i++)   
      for (int k=0;k<4;k++)   
     if (a[ii[i] +x[k]][jj[i] +y[k]]==0 ){   
       a[ii[i] +x[k]][jj[i] +y[k]] = a[ii[i]][jj[i]]+1;   
       ii[nr]=ii[i]+x[k];   
       jj[nr]=jj[i]+y[k];   
       nr++;   
   }   
}   
  
void fct()   
{   
   int max=n;   
   if (m>n)   
      max=m;   
  
   for (int r=0;r<=max;r++)   
   {   
      a[r][0]=-1;   
      a[r][m+1]=-1;   
      a[n+1][r]=-1;   
      a[0][r]=-1;   
   }   
   lee();   
}   
  
  
int da(int ups)   
{   
    memset(b,0,sizeof(b));   
    ii[0]=xi;   
    jj[0]=yi;   
    int nr=0;   
    if (a[xi][yi]>=ups){   
       b[xi][yi]=1;   
        nr=1;   
    }   
    for ( int i=0;i<nr;i++)   
          for ( int k=0;k<4;k++)   
              if (a[ii[i] +x[k]][jj[i] +y[k]]>=ups&& b[ii[i]+x[k]][jj[i]+y[k]]==0)   
              {   
                    b[ii[i] +x[k]][jj[i] +y[k]]=1;   
                    ii[nr]=ii[i]+x[k];   
                    jj[nr]=jj[i]+y[k];   
                    nr++;   
              }   
return b[xf][yf];   
}   
void caut()   
{   
  
     int max=-1;   
     for (int q=1;q<=n;q++)   
            for (int w=1;w<=m;w++)   
                  if (a[q][w]>max)   
                         max=a[q][w];   
    minim=max;   
    for (int v=max;v>=0;v--)   
        if (da(v))   
        {   
              minim=v;   
              return;   
        }   
}   
  
  
void okk()   
{   
     int nr=0;   
    ii[0]=xi;   
	memset(b,0,sizeof(b));
    jj[0]=yi;   
    a[xi][yi]=1;   
	b[xi][yi]=1;
    for (int i=0;i<nr;i++)   
           for (int k=0;k<4;k++)   
               if (a[ii[i] +x[k]][jj[i] +y[k]]!=-1 && b[ii[i] +x[k]][jj[i] +y[k]]==0)   
               {   
				   b[ii[i]+x[k]][jj[i]+y[k]]=1;
                   a[ii[i] +x[k]][jj[i] +y[k]]=-2;   
                   ii[nr]=ii[i]+x[k];   
                   jj[nr]=jj[i]+y[k];   
                   nr++;   
               }   
}   
  
int main ()   
{   
       minim=0;   
   citire();   
   fct();   
   caut();  
   okk();   
  if (a[xf][yf]==-2)   
      fout<<"-1\n";   
  else  
          fout<<minim-1<<"\n";   
   fout.close();   
   return 0;   
}