#include <cstdio>
#include <queue>
using namespace std;
const int nmax = 1005;
int dx[]={-1, 0, 1, 0};
int dy[]={0, 1, 0, -1};
int mat[nmax][nmax], n, m, ix, ox, iy, oy, i, j;
bool ok[nmax][nmax], sol, gasit;
queue < pair<int,int> > q;
void lee_dragoni()
{
    while(!q.empty())
    {
        int nx=q.front().first;
        int ny=q.front().second;
        q.pop();
        for(i=0; i<4; i++)
        {
            int xx=nx+dx[i];
            int yy=ny+dy[i];
            if(xx<=n && xx>0 && yy<=m && yy>0 && !mat[xx][yy])
            {
                q.push(make_pair(xx,yy));
                mat[xx][yy]=mat[nx][ny]+1;
            }
        }
    }
}
bool lee_okay(int mid)
{
    q.push(make_pair(ix,iy));
    ok[ix][iy]=1;
    while(!q.empty() && !gasit)
    {
        int nx=q.front().first;
        int ny=q.front().second;
        q.pop();
        for(i=0; i<4; i++)
        {
            int xx=nx+dx[i];
            int yy=ny+dy[i];
            if(xx<=n && xx>0 && yy<=m && yy>0 && mat[xx][yy]>=mid && !ok[xx][yy])
            {
                q.push(make_pair(xx,yy));
                ok[xx][yy]=1;
                if(xx==ox && yy==oy) return 1;
            }
        }
    }
    return 0;
}
int main()
{
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);
    scanf("%d %d\n", &n, &m);
    for(i=1; i<=n; i++, scanf("\n"))
        for(j=1; j<=m; j++)
        {
            char ch;
            scanf("%c", &ch);
            if(ch=='*') mat[i][j]=-1;
            else if(ch=='D')
            {
                q.push(make_pair(i,j));
                mat[i][j]=1;
            }
            else if(ch=='I') ix=i, iy=j;
            else if(ch=='O') ox=i, oy=j;
        }
    lee_dragoni();
    int st=1, dr=n*m;
    for(i=1; i<=n; i++)
        for(j=1; j<=m; j++)
        {
            if(mat[i][j]!=-1) ok[i][j]=0;
            else ok[i][j]=1;
        }
    while(st<=dr)
    {
        int mid=(st+dr)/2;
        if(lee_okay(mid) && mat[ix][iy]>=mid)
        {
            st=mid+1;
            sol=1;
        }
        else dr=mid-1;
    }
    if(sol) printf("%d\n", dr-1);
    else printf("-1");
    fclose(stdin);
    fclose(stdout);
    return 0;
}