# include <fstream>
# define DIM 1010
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int di[]={0,0,1,-1};
int dj[]={1,-1,0,0};
unsigned char c[2][DIM*DIM+1],x;
int ok,v[DIM][DIM],i,j,n,iv,jv,f[DIM][DIM],ic,jc,u,p,d,m,is,js,ifin,jfin,st,dr,mij;
int main  () {
    fin>>n>>m;
    for(i=1;i<=n;i++){
        for(j=1;j<=m;j++){
            fin>>x;
            if(x=='I'){
                is=i;
                js=j;
            }
            if(x=='O'){
                ifin=i;
                jfin=j;
            }
            if(x=='*')
                v[i][j]=-1;
            if(x=='D'){
                c[0][++u]=i;
                c[1][u]=j;
                v[i][j]=1;
            }
        }
    }
    p=1;
    while(p<=u){
        ic=c[0][p];
        jc=c[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&&v[iv][jv]==0){
                c[0][++u]=iv;
                c[1][u]=jv;
                v[iv][jv]=v[ic][jc]+1;
            }
        }
        p++;
    }
    for(i=1;i<=n;i++){
        for(j=1;j<=n;j++){
            v[i][j]--;
        }
    }
    st=1;
    dr=min(v[is][js],v[ifin][jfin])-1;
    while(st<=dr){
        mij=(st+dr)/2;
        p=1;
        u=1;
        c[0][1]=is;
        c[1][1]=js;
        for(i=1;i<=n;i++){
            for(j=1;j<=m;j++)
                f[i][j]=0;
        }
        f[is][js]=1;
        while(p<=u){
            ic=c[0][p];
            jc=c[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&&v[iv][jv]>=mij&&f[iv][jv]==0){
                    f[iv][jv]=1;
                    u++;
                    c[0][u]=iv;
                    c[1][u]=jv;
                }
            }
                p++;
        }
        if(f[ifin][jfin]!=0)
            st=mij+1;
        else
            dr=mij-1;
    }
    if(dr<1)
        dr=-1;
    fout<<dr<<"\n";
    return 0;
}