#include <iostream>
#include <fstream>
#include <queue>

using namespace std;
ifstream r("barbar.in");
ofstream w("barbar.out");
int matrice[1002][1002], cm[1002][1002];
struct qu
{
    int x, y;
};
queue<qu>q;
int main()
{
    int m, n, li, ci, lf, cf;
    qu nod;
    r>>m>>n;
    r.get();
    for(int i=1; i<=m; i++)
    {
        for(int j=1; j<=n; j++)
        {
            char c;
            c=r.get();
            if(c=='*')
            {
                matrice[i][j]=-2;
            }
            if(c=='I')
            {
                li=i;
                ci=j;
            }
            if(c=='O')
            {
                lf=i;
                cf=j;
            }
            if(c=='D')
            {
                matrice[i][j]=1;
                nod.x=i;
                nod.y=j;
                q.push(nod);
            }
        }
        r.get();
    }
    while(q.size()!=0)
    {
        int l=q.front().x, c=q.front().y;
        if(l-1>0 && matrice[l-1][c]==0)
        {
            matrice[l-1][c]=matrice[l][c]+1;
            nod.x=l-1;
            nod.y=c;
            q.push(nod);
        }
        if(c-1>0 && matrice[l][c-1]==0)
        {
            matrice[l][c-1]=matrice[l][c]+1;
            nod.x=l;
            nod.y=c-1;
            q.push(nod);
        }
        if(l+1<=m && matrice[l+1][c]==0)
        {
            matrice[l+1][c]=matrice[l][c]+1;
            nod.x=l+1;
            nod.y=c;
            q.push(nod);
        }
        if(c+1<=n && matrice[l][c+1]==0)
        {
            matrice[l][c+1]=matrice[l][c]+1;
            nod.x=l;
            nod.y=c+1;
            q.push(nod);
        }
        q.pop();
    }
    int st=0, dr=1000, mij, p=-1;
    while(st<=dr)
    {
        mij=(dr+st)/2;
        nod.x=li;
        nod.y=ci;
        q.push(nod);
        for(int i=1;i<=m;i++){
            for(int j=1;j<=n;j++){
                cm[i][j]=matrice[i][j];
            }
        }
        while(q.size()!=0)
        {
            int l=q.front().x, c=q.front().y;
            if(l-1>0 && cm[l-1][c]>mij)
            {
                cm[l-1][c]=0;
                nod.x=l-1;
                nod.y=c;
                q.push(nod);
            }
            if(c-1>0 && cm[l][c-1]>mij)
            {
                cm[l][c-1]=0;
                nod.x=l;
                nod.y=c-1;
                q.push(nod);
            }
            if(l+1<=m && cm[l+1][c]>mij)
            {
                cm[l+1][c]=0;
                nod.x=l+1;
                nod.y=c;
                q.push(nod);
            }
            if(c+1<=n && cm[l][c+1]>mij)
            {
                cm[l][c+1]=0;
                nod.x=l;
                nod.y=c+1;
                q.push(nod);
            }
            q.pop();
        }
        if(cm[lf][cf]==0 && matrice[li][ci]>mij){
            st=mij+1;
            p=mij;
        }
        else{
            dr=mij-1;
        }
    }
        w<<p;
    return 0;
}