#include <fstream>
#include <cstring>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int n,i,j,st,dr,sol,mid,a[1005][1005],x1,y1,x2,y2,p,u,l,c,m,x,y;
bool b[1005][1005];
int dx[]={-1,1,0,0};
int dy[]={0,0,-1,1};
char xx;
short q[2][1000*1000+5];
int verif(int mid){
    q[0][1]=x1;
    q[1][1]=y1;
    int ok = 0;
    if(a[x1][y1]>=mid){
        memset(b,0,sizeof(b));
        int p,u,c,l,x,y;
        p=1;u=1;
        b[x1][y1]=1;
        while(p<=u){
            x=q[0][p];
            y=q[1][p];
            for(i=0;i<4;i++){
                l=x+dx[i];
                c=y+dy[i];
                if(a[l][c]>=mid && a[l][c]!=-1  && b[l][c]==false && l>=1 && l<=n && c>=1 && c<=m){
                    b[l][c]=1;
                    u++;
                    q[0][u]=l;
                    q[1][u]=c;
                    if(l==x2 && c==y2){
                        ok=1;
                        break;
                    }

                }

            }
            if(ok==1){
                return 1;
            }
            p++;
        }
    }
    return 0;
}
int main(){
    fin>>n>>m;
    for(i=1;i<=n;i++){
        for(j=1;j<=m;j++){
            fin>>xx;
            if(xx=='*'){
                a[i][j]=-1;
            }
            if(xx=='D'){
                q[0][++u]=i;
                q[1][u]=j;
                a[i][j]=1;
                b[i][j]=1;
            }
            if(xx=='I'){
                x1=i;
                y1=j;
            }
            if(xx=='O'){
                x2=i;y2=j;
            }
        }
    }
    p=1;
    while(p<=u){
        x=q[0][p];
        y=q[1][p];
        for(i=0;i<4;i++){
            l=x+dx[i];
            c=y+dy[i];
            if(a[l][c]==0 && l>=1 && l<=n && c>=1 && c<=m){
                a[l][c]=a[x][y]+1;
                u++;
                q[0][u]=l;
                q[1][u]=c;
            }
        }
        p++;
    }
    st=1;
    dr=n*m;
    while(st<=dr){
        mid=(st+dr)/2;
        if(verif(mid)){
            st=mid+1;
            sol=mid;
        }
        else{
            dr=mid-1;
        }
    }
    if(sol==0){
        fout<<-1<<"\n";
    }
    else{
        fout<<sol-1<<"\n";
    }




    return 0;
}