const f='barbar.in'; g='barbar.out';
const dx:array[0..3]of shortint=(-1,0,1,0);
const dy:array[0..3]of shortint=(0,1,0,-1);
type elem=record
x,y:longint;
end;
var
drum:array[0..1000000]of elem;
a,x:array[0..1001,0..1001]of longint;
xp,xs,yp,ys,r,c,i,j:longint;
ch:char;
dr:longint;
ince,sf:elem;
function check(x,y:longint):boolean;
begin
if (x>=1)and(x<=r)and(y>=1)and(y<=c)then check:=true
else check:=false;
end;
procedure lee;
var
st,k,ii,jj:longint;
begin
st:=1;
a[drum[st].x,drum[st].y]:=0;
while(st<=dr)do begin
for k:=0 to 3 do begin
ii:=drum[st].x+dx[k];
jj:=drum[st].y+dy[k];
if(check(ii,jj))and (a[ii,jj]=-2)then begin
inc(dr);
drum[dr].x:=ii;
drum[dr].y:=jj;
a[ii,jj]:=a[drum[st].x,drum[st].y]+1;
end;
end;
inc(st);
end;
end;
function posibil(d:longint):boolean;
var
st,k,ii,jj:longint;
begin
posibil:=false;
fillchar(x,sizeof(x),0);
st:=1;dr:=1;
drum[st]:=ince;
x[drum[st].x,drum[st].y]:=1;
while (st<=dr) do begin
for k:=0 to 3 do begin
ii:=drum[st].x+dx[k];
jj:=drum[st].y+dy[k];
if (check(ii,jj))and(a[ii,jj]>=d)and(x[ii,jj]=0)then begin
inc(dr);
drum[dr].x:=ii;
drum[dr].y:=jj;
x[ii,jj]:=1;
end;
end;
inc(st);
end;
if x[sf.x,sf.y]=1 then posibil:=true;
end;
function solve(ls,ld:longint):longint;
var
st,dr,mij,sol:longint;
begin
st:=ls;
dr:=ld;
while (st<=dr)do begin
mij:=(st+dr)div 2;
if posibil(mij)then begin
st:=mij+1;
sol:=mij;
end
else dr:=mij-1;
end;
if (sol>0) then solve:=sol else solve:=-1;
end;

begin
assign(input,f);reset(input);
assign(output,g);rewrite(output);
readln(r,c);
for i:=1 to r do begin
for j:=1 to c do begin
read(ch);
if ch='D'then begin
inc(dr);
drum[dr].x:=i; drum[dr].y:=j;
a[i,j]:=0;
end;
if (ch='I')then begin a[i,j]:=-2;ince.x:=i;ince.y:=j; end;
if (ch='O')then begin a[i,j]:=-2;sf.x:=i;sf.y:=j;end;
if (ch='*')then a[i,j]:=-1;
if (ch='.')then a[i,j]:=-2;
end;
readln;
end;
lee;
writeln(solve(-1,a[ince.x,ince.y]));
end.