#include<cstdio>
#include<cstring>
#include<algorithm>
#include<deque>
using namespace std;
const int nmax=1000;
int px[10],py[10];
char si[nmax+5][nmax+5];
int n,m,dist[nmax][nmax+5];
bool viz[nmax+5][nmax+5];
deque<pair<int,int> > dq;
bool bfs(pair<int,int> init,int d,pair<int,int> dest)
{
    int i,x,y;
    pair<int,int> tm;
    dq.push_back(init);
    viz[init.first][init.second]=1;
    while(!dq.empty())
    {
        tm=dq.front();
        dq.pop_front();

    for(i=1;i<=4;i++)
    {
        x=tm.first+px[i];
        y=tm.second+py[i];
        if(viz[x][y]==0 && (si[x][y]=='.' || si[x][y]=='O' || si[x][y]=='D') && dist[x][y]>=d)
        {
            viz[x][y]=1;
            dq.push_back(make_pair(x,y));
        }
    }

    }
    if(viz[dest.first][dest.second] && dist[init.first][init.second]>=d)
        return 1;
    else
        return 0;
}
int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    int x,y,i,j,d;
    pair<int,int > tm,init,dest;
    px[1]=1;px[2]=0;px[3]=-1;px[4]=0;
    py[1]=0;py[2]=-1;py[3]=0;py[4]=1;
    scanf("%d%d\n",&n,&m);
    for(i=1;i<=n;i++)
      gets(si[i]+1);
    for(i=1;i<=n;i++)
        dist[i][0]=dist[i][m+1]=-1;
    for(i=1;i<=m;i++)
        dist[0][i]=dist[n+1][i]=-1;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
        {
              if(si[i][j]=='D')
              {
                   dist[i][j]=0;
                   dq.push_back(make_pair(i,j));
              }
              if(si[i][j]=='I')
              {
                  init=make_pair(i,j);
              }
              if(si[i][j]=='*')
              {
                  dist[i][j]=0;
              }
              if(si[i][j]=='O')
              {
                  dest.first=i;
                  dest.second=j;
              }
              if(si[i][j]=='*')
              {
                  dist[i][j]=-1;
              }
        }
        while(!dq.empty())
        {
           tm=dq.front();
           dq.pop_front();
           d=max(dist[tm.first][tm.second],0);
           for(i=1;i<=4;i++)
           {
               x=tm.first+px[i];
               y=tm.second+py[i];
            if(dist[x][y]==0 && (si[x][y]=='I' || si[x][y]=='.' || si[x][y]=='O'))
           {
               dist[x][y]=d+1;
               dq.push_back(make_pair(x,y));
           }
           }
        }
        /*for(i=1;i<=n;i++)
        {
            for(j=1;j<=m;j++)
        {
            printf("%d ",dist[i][j]);
        }
        printf("\n");
        }*/
        int st,dr,mi,la;
        st=0;
        dr=n*m;
        la=-1;
        while(st<=dr)
        {
            mi=(st+dr)/2;
            if(bfs(init,mi,dest))
            {
                la=mi;
                st=mi+1;
            }
            else
            {
                dr=mi-1;
            }
            for(i=1;i<=n;i++)
            for(j=1;j<=m;j++)
            viz[i][j]=0;
        }
    printf("%d\n",la);
    return 0;
}