#include <fstream>
#define valid(x1,y1) x1&&y1>-1&&x1<=n&&y1<m
using namespace std;
int const dirx[]={0,1,0,-1}, diry[]={1,0,-1,0},dim=1001;
char mat[dim][dim];
int v[dim][dim], st, dr, n, m;
bool b[dim][dim],viz[dim][dim];
struct bar{
    int a, b;
}q[dim*dim];
bool pot(int dist,bar i,bar o){
    st=dr=1;
    q[1]={i.a,i.b};
    if(v[i.a][i.b]<dist)
        return 0;
    while(st<=dr){
        int x=q[st].a;
        int y=q[st].b;
        for(int i=0;i<4;i++){
            int x1=x+dirx[i];
            int y1=y+diry[i];
            if(x1==o.a&&y1==o.b){
                if(v[x1][y1]<dist)
                    return 0;
                return 1;
            }
            if(b[x1][y1]==0&&v[x1][y1]>=dist&&viz[x1][y1]==0&&valid(x1,y1)){
                q[++dr]={x1,y1};
                viz[x1][y1]=1;
            }
        }
        st++;
    }
    return 0;
}
int main()
{
    freopen ("barbar.in","r",stdin);
    freopen ("barbar.out","w",stdout);
    int i,j,mx=0;
    bar in,o;
    scanf("%d%d",&n,&m);
    for(i=1;i<=n;i++)
        scanf("%s",&mat[i]);
    for(i=1;i<=n;i++)
        for(j=0;j<m;j++){
            if(mat[i][j]=='I')
                in={i,j};
            if(mat[i][j]=='O')
                o={i,j};
            if(mat[i][j]=='D')
                q[++dr]={i,j};
            if(mat[i][j]=='*')
                b[i][j]=1;
        }
    st=1;
    while(st<=dr){
        int x=q[st].a;
        int y=q[st].b;
        for(i=0;i<4;i++){
            int x1=x+dirx[i];
            int y1=y+diry[i];
            if(b[x1][y1]==0&&v[x1][y1]==0&&valid(x1,y1)){
                v[x1][y1]=1+v[x][y];
                mx=max(mx,v[x1][y1]);
                q[++dr]={x1,y1};
            }
        }
        st++;
    }
    int s=1,d=mx,r=-1;
    while(s<=d){
        int mij=(s+d)/2;
        if(pot(mij,in,o)==1)
            s=mij+1,r=mij;
        else
            d=mij-1;
    }
    printf("%d",r);
    return 0;
}