#include <fstream>
#include <queue>
#include <cstring>
using namespace std;
ifstream cin("barbar.in");
ofstream cout("barbar.out");
int n,m,i,j,ii,ji,io,jo,a[1005][1005],d[1005][1005],dx[]={0,-1,0,1,0},dy[]={0,0,1,0,-1};
bool viz[1005][1005];
struct coada{
   int l,c;
};
queue<coada>q;
char ch;
bool bfs(int dis){
    while(!q.empty())
        q.pop();
    if(d[ii][ji]<=dis)
        return 0;
    memset(viz,0,sizeof(viz));
    q.push({ii,ji});
    viz[ii][ji]=1;
    while(!q.empty())
    {
        int l=q.front().l,c=q.front().c;
        for(i=1;i<=4;i++)
        {
            int lv=l+dx[i],cv=c+dy[i];
            if(viz[lv][cv]==0&&lv>0&&cv>0&&lv<=n&&cv<=m&&d[lv][cv]>dis)
            {
                q.push({lv,cv});
                viz[lv][cv]=1;
                if(lv==io&cv==jo)
                    return 1;
            }
        }
        q.pop();
    }
    return 0;
}
int main()
{
    cin>>n>>m;
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++){
            cin>>ch;
            if(ch=='I')
            {
                ii=i,ji=j;
            }
            else
                if(ch=='O')
                io=i,jo=j;
            else
                if(ch=='D')
            {
                q.push({i,j});
                d[i][j]=1;
            }
            else
                if(ch=='*')
                a[i][j]=-1;
        }
    while(!q.empty())
    {
        int l=q.front().l,c=q.front().c;
        for(i=1;i<=4;i++)
        {
            int lv=l+dx[i],cv=c+dy[i];
            if(d[lv][cv]==0&&a[lv][cv]==0&&lv>0&&cv>0&&lv<=n&&cv<=m)
            {
                q.push({lv,cv});
                d[lv][cv]=d[l][c]+1;
            }
        }
        q.pop();
    }
    int st=0,dr=n*m,sol=-1;
    while(st<=dr)
    {
        int mid=(st+dr)/2;
        if(bfs(mid)==1)
            {
                sol=mid;
                st=mid+1;
            }
        else
            dr=mid-1;
    }
    cout<<sol;
    return 0;
}