#include <fstream>
#include <queue>
using namespace std;
ifstream in("barbar.in");
ofstream out("barbar.out");
struct data {
  short int x,y;
  short int worst;
  bool operator <(const data& x) const {
    return worst<x.worst;
  }
};
static data makedata(int x,int y, int worst) {
  data rez;
  rez.x=x;
  rez.y=y;
  rez.worst=worst;
  return rez;
}
priority_queue<data> pq;
queue <data> q;
int rez;
int mat[1002][1002],startx,starty,endx,endy;
int dirx[4]={1,-1,0,0};
int diry[4]={0,0,1,-1};
void findroad() {
  if(pq.empty())
    return;
  int x=pq.top().x,y=pq.top().y,worst=pq.top().worst;
  pq.pop();
  mat[x][y]=-1;
  if(endx==x && endy==y) {
    while(!pq.empty())
      pq.pop();
    if(worst==1)
      worst==0;
    rez=worst-1;
  }
  else {
    for(int i=0; i<4; i++) {
      if(mat[x+dirx[i]][y+diry[i]]!=-1)
        pq.push(makedata(x+dirx[i],y+diry[i],min(worst,mat[x+dirx[i]][y+diry[i]])));
    }
  }
  findroad();
  return;
}
void setup() {
  if(q.empty())
    return;
  int x=q.front().x,y=q.front().y,worst=q.front().worst;
  q.pop();
  for(int i=0; i<4; i++) {
    if(mat[x+dirx[i]][y+diry[i]]==0) {
      mat[x+dirx[i]][y+diry[i]]=worst+1;
      q.push(makedata(x+dirx[i],y+diry[i],worst+1));
    }
  }
  setup();
  return;
}
int main()
{
  int n,m;
  char ch;
  in >> n >> m;
  for(int i=0; i<=n+1; i++)
    mat[i][0]=mat[i][m+1]=-1;
  for(int i=0; i<=m+1; i++)
    mat[0][i]=mat[n+1][i]=-1;
  for(int i=1; i<=n; i++) {
    for(int j=1; j<=m; j++) {
      in >> ch;
      if(ch=='*')
        mat[i][j]=-1;
      else if(ch=='I') {
        startx=i;
        starty=j;
      }
      else if(ch=='O') {
        endx=i;
        endy=i;
      }
      else if(ch=='D') {
        mat[i][j]=1;
        q.push(makedata(i,j,1));
      }
    }
  }
  setup();
  pq.push(makedata(startx,starty,mat[startx][starty]));
  rez=-1;
  findroad();
  out << rez;
  return 0;
}