#include<fstream>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int di[]={0,0,-1,1};
int dj[]={-1,1,0,0};
int i,j,n,m,d,iv,jv,ic,jc,u,p,is,js,ifi,jf,st,dr,mid,a[1005][1005],b[1005][1005],s[2][1000005];
char k;
int main(){
    fin>>n>>m;
    for(i=1;i<=n;i++){
        for(j=1;j<=m;j++){
            fin>>k;
            if(k=='I'){
                is=i;
                js=j;
            }
            if(k=='O'){
                ifi=i;
                jf=j;
            }
            if(k=='*'){
                a[i][j]=-1;
                b[i][j]=-1;
            }
            if(k=='D'){
                s[0][++u]=i;
                s[1][u]=j;
                a[i][j]=1;
            }
        }
    }
    p=1;
    while(p<=u){
        ic=s[0][p];
        jc=s[1][p];
        for(d=0;d<=3;d++){
            iv=ic+di[d];
            jv=jc+dj[d];
            if(iv<=n&&iv>=1&&jv<=m&&jv>=1&&a[iv][jv]==0){
                s[0][++u]=iv;
                s[1][u]=jv;
                a[iv][jv]=a[ic][jc]+1;
            }
        }
        p++;
    }
    st=1;
    dr=100005;
    while(st<=dr){
        mid=(st+dr)/2;
        p=1;
        u=1;
        s[0][1]=is;
        s[1][1]=js;
        for(i=1;i<=n;i++){
            for(j=1;j<=n;j++){
                b[i][j]=0;
            }
        }
        b[is][js]=1;
        while(p<=u){
            ic=s[0][p];
            jc=s[1][p];
            for(d=0;d<=3;d++){
                iv=ic+di[d];
                jv=jc+dj[d];
                if(iv>=1&&iv<=n&&jv>=1&&jv<=m&&a[iv][jv]>mid&&b[iv][jv]==0){
                    b[iv][jv]=1;
                    u++;
                    s[0][u]=iv;
                    s[1][u]=jv;
                }
            }
            p++;
        }
        if(b[ifi][jf]==0){
            dr=mid-1;
        }
        else{
            st=mid+1;
        }
    }
    if(dr<=0){
        fout<<"-1";
        return 0;
    }
    fout<<dr;
    return 0;
}