#include <fstream>
#include <algorithm>
#include <queue>
#include <cstring>

#define nmax 1010

using namespace std;

ifstream in("barbar.in");
ofstream out("barbar.out");

int N,M;
int A[nmax][nmax],D[nmax][nmax],VIZ[nmax][nmax];
int dl[]= {0,1,0,-1};
int dc[]= {-1,0,1,0};
struct nod
{
    int x,y;
} start, stop, temp, nou;
queue <nod> q;

bool traseu(int p)
{
    if(D[start.x][start.y]<p) return 0;
    q.push(start);
    memset(VIZ,0,sizeof(VIZ));
    VIZ[start.x][start.y]=1;
    while(!q.empty())
    {
        temp=q.front();
        q.pop();
        for(int lin,col,k=0; k<4; ++k)
        {
            lin =temp.x+dl[k];
            col =temp.y+dc[k];
            if(D[lin][col]>=p && !VIZ[lin][col])
            {
                VIZ[lin][col]=1;
                nou.x=lin;
                nou.y=col;
                q.push(nou);
            }
        }
    }
    return VIZ[stop.x][stop.y];
}

void init()
{
    for(int i=1; i<=N; ++i)
        for(int j=1; j<=M; ++j)
            D[i][j]=-2;
}

void bordare()
{
    for(int i=0; i<=N+1; ++i) D[i][0]=D[i][M+1]=-1;
    for(int i=0; i<=M+1; ++i) D[0][i]=D[N+1][i]=-1;
}

void citire()
{
    char ch;
    in>>N>>M;
    init();
    bordare();
    for(int i=1; i<=N; ++i)
        for(int j=1; j<=M; ++j)
        {
            in>>ch;
            switch(ch)
            {
            case '*' :
                D[i][j]=-1;
                break;
            case 'O' :
                stop.x=i;
                stop.y=j;
                break;
            case 'I' :
                start.x=i;
                start.y=j;
                break;
            case 'D' :
                D[i][j]=0;
                nou.x=i;
                nou.y=j;
                q.push(nou);
                break;
            }
        }
}

void LEE()
{
    while(!q.empty())
    {
        temp=q.front();
        q.pop();
        for(int lin,col,k=0; k<4; ++k)
        {
            lin=temp.x+dl[k];
            col=temp.y+dc[k];
            if(D[lin][col]==-2)
            {
                D[lin][col]=D[temp.x][temp.y]+1;
                nou.x=lin;
                nou.y=col;
                q.push(nou);
            }
        }
    }
}

void caut_bin(int &dist)
{
    if(D[start.x][start.y] !=-2)
    {
        int st=0, dr=N*M, mij;
        while(st<=dr)
        {
            mij=(st+dr)>>1;
            if(traseu(mij))
            {
                dist=mij;
                st=mij+1;
            }
            else dr=mij-1;
        }
    }
}

int main()
{
    citire();
    LEE(); //Lee plecand de la dragoni
    int dist=-1;
    caut_bin(dist);
    out<<dist<<'\n';
    return 0;
}