#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int u,dx[]={0,-1,0,1,0},dy[]={0,0,1,0,-1},r,c,i,j,p1,p2,a1,a2,a[1002][1002],b[1001][1001],q[2][1000002];
char x;
bool Viz[1001][1001];
void coadad(){
     int p=1,l,c,ln,cn,i;
     while(p<=u){
           l=q[0][p];
           c=q[1][p];
           p++;
           for(i=1;i<=4;i++){
               ln=l+dx[i];
               cn=c+dy[i];
               if(a[ln][cn]==0&&b[ln][cn]==0){
                  b[ln][cn]=b[l][c]+1;
                  q[0][++u]=ln;
                  q[1][u]=cn;
               }
           }
     }
}
int  coada(int x, int y,int d){
           int p,u,i,l,c,ln,cn;
           memset(Viz,0,sizeof(Viz));
           p=u=1;
           q[0][p]=x;
           q[1][p]=y;
           if(b[x][y]<d)
              return 0;
           Viz[x][y]=1;
           while(p<=u&&Viz[a1][a2]==0){
                 l=q[0][p];
                 c=q[1][p];
                 p++;
                 for(i=1;i<=4;i++){
                     ln=l+dx[i];
                     cn=c+dy[i];
                     if(a[ln][cn]==0&&b[ln][cn]>=d&&Viz[ln][cn]==0){
                        Viz[ln][cn]=1;
                        q[0][++u]=ln;
                        q[1][u]=cn;
                     }
                 }
           }
   return Viz[a1][a2]==1;
}
int main()
{fin>>r>>c;
for(i=1;i<=r;i++)
    for(j=1;j<=c;j++){
        fin>>x;
        if(x=='*')
           a[i][j]=1;
        else
           if(x=='D'){
              a[i][j]=1;
              u++;
              q[0][u]=i;
              q[1][u]=j;  }
           else
              if(x=='I')
                 p1=i,p2=j;
               else
                    if(x=='O')
                       a1=i,a2=j;
    }
for(i=0;i<=c+1;i++)
    a[0][i]=a[r+1][i]=1;
for(i=0;i<=r+1;i++)
    a[i][0]=a[i][c+1]=1;

coadad();
int st=0, dr=max(r,c);
int sol=-1;
while(st<=dr){
    int mid=(st+dr)/2;
    int k=coada(p1,p2,mid);
    if(k==1){
        sol=mid;
        st=mid+1;
    }
    else
        dr=mid-1;
}

fout<<sol;








return 0;
}