#include<stdio.h>
#include<stdlib.h>
#define MAXINT 32000
int r,c,val=0,ok=1,xo,yo,sch=0,cont,prim,p,indr=-1;
struct ghj
{
   short val,init;
}a[1002][1002];
struct nod
{
   short x,y,val;
}v[40160000],dr[1000000];
void adauga(int i,int j);
void adaugaI(int i,int j);
int main()
{  //clrscr();

   FILE*f=fopen("barbar.in","r");
   fscanf(f,"%d%d",&r,&c);
   int i,j,xi,yi;

   char var;
   for(i=0;i<=r+1;++i)
   for(j=0;j<=c+1;++j)
   {
	   if(!i||!j||i==r+1||j==c+1){a[i][j].init=a[i][j].val=-MAXINT;continue;}
	   fscanf(f,"%c",&var);
	   if(var=='\n'){j--;continue;}
	   switch(var)
	   {
		  case '.':{a[i][j].init=a[i][j].val=MAXINT;break;}
		  case '*':{a[i][j].init=a[i][j].val=-MAXINT;break;}
		  case 'I':{a[i][j].init=a[i][j].val=MAXINT;xi=i;yi=j;break;}
		  case 'O':{a[i][j].init=a[i][j].val=MAXINT;xo=i;yo=j;break;}
		  case 'D':{
					  a[i][j].init=a[i][j].val=0;
					  ++indr;
					  dr[indr].x=i;
					  dr[indr].y=j;
					  dr[indr].val=0;
					  break;
				   }
	   }
   }
   fclose(f);

   int contor=0;
   while(indr>=0)
   {
	prim=0;
	cont=1;
	--indr;
	v[cont].x=dr[indr].x;
	v[cont].y=dr[indr].y;
	v[cont].val=dr[val].val;
	v[cont+1].val=-1;
   while(v[prim+1].val>-1)
   {
	  p=prim+1;
	  val=v[p].val+1;
	  i=v[p].x;
	  j=v[p].y;
	  prim=p;
	  
	  contor=0;
	  while(contor<4)
	  {
		 switch(contor)
		 {
			case 0:{adauga(i-1,j);break;}
			case 1:{adauga(i+1,j);break;}
			case 2:{adauga(i,j-1);break;}
			case 3:{adauga(i,j+1);break;}
		 }
		 ++contor;
	  }
   }
   }
   if(a[xi][yi].val<a[xo][yo].val)val=a[xi][yi].val;
   else val=a[xo][yo].val;
   ok=1;if(val%2)sch=1;
   if(a[xi][yi].val==MAXINT||a[xo][yo].val==MAXINT)val=-1;

   prim=cont=0;
   for(;val>=0&&ok;--val)
   {
	   ++cont;
	   v[cont].x=xi;v[cont].y=yi;v[cont].val=0;
	   while(v[prim+1].val>-1&&ok)
	   {
		  p=prim+1;
		  prim=p;
		  i=v[p].x;
		  j=v[p].y;
		  contor=0;
		  while(contor<4)
		  {
			  switch(contor)
			  {
				case 0:{adaugaI(i-1,j);break;}
				case 1:{adaugaI(i+1,j);break;}
				case 2:{adaugaI(i,j-1);break;}
				case 3:{adaugaI(i,j+1);break;}
			  }
			  ++contor;
		  }
	  }
	  sch=!sch;
   }

   FILE*g=fopen("barbar.out","w");
   if(!ok)fprintf(g,"%d",val+1);
   else	fprintf(g,"-1");
   fclose(g);
   return 0;
}
void adauga(int i,int j)
{
	if(a[i][j].val>val)
	{
	   ++cont;
	   v[cont].x=i;
	   v[cont].y=j;
	   v[cont].val=val;
	   v[cont+1].val=-1;
	   a[i][j].val=a[i][j].init=val;
	}
}
void adaugaI(int i,int j)
{
	if((a[i][j].val>=val&&sch)||(a[i][j].init>=val&&!sch))
	{  if(i==xo&&j==yo){ok=0;}
	   ++cont;
	   v[cont].x=i;
	   v[cont].y=j;
	   v[cont].val=1;
	   if(sch){a[i][j].val*=-1;a[i][j].init=abs(a[i][j].init);}
	   if(!sch){a[i][j].init*=-1;a[i][j].val=abs(a[i][j].val);}
	   v[cont+1].val=-1;
	}
}