#include <bits/stdc++.h>

using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int NMAX=1005, inf=2e9;

///dist[i][j]=ditanta pana la cel mai apropiat dragon din celula (i,j)
int N, M, dist[NMAX][NMAX], dl[]={-1,0,1,0}, dc[]={0,1,0,-1};
char mat[NMAX][NMAX];
bool viz[NMAX][NMAX];
struct punct{
    int x, y;
};
punct start, finish;
queue<punct> q;

bool inMatrix(int x, int y){
    return x>=1 and x<=N and y>=1 and y<=M;
}

void computeDistance(){
    punct p;
    while(!q.empty()){
        p=q.front();
        q.pop();
        for(int k=0;k<4;k++){
            if(inMatrix(p.x+dl[k],p.y+dc[k]) and viz[p.x+dl[k]][p.y+dc[k]]==false){
                viz[p.x+dl[k]][p.y+dc[k]]=true;
                dist[p.x+dl[k]][p.y+dc[k]]=dist[p.x][p.y]+1;
                q.push({p.x+dl[k],p.y+dc[k]});
            }
        }
    }
}

bool verificare(int d){
    if(dist[start.x][start.y]<d)
        return 0;
    while(!q.empty())
        q.pop();
    for(int i=1;i<=N;i++)
        for(int j=1;j<=M;j++)
            viz[i][j]=false;

    q.push({start.x,start.y});
    viz[start.x][start.y]=true;
    punct p;
    while(!q.empty()){
        p=q.front();
        q.pop();
        if(p.x==finish.x and p.y==finish.y)
            return 1;
        for(int k=0;k<4;k++){
            if(inMatrix(p.x+dl[k],p.y+dc[k])){
                if(mat[p.x+dl[k]][p.y+dc[k]]!='*' and dist[p.x+dl[k]][p.y+dc[k]]>=d and viz[p.x+dl[k]][p.y+dc[k]]==false){
                    viz[p.x+dl[k]][p.y+dc[k]]=true;
                    q.push({p.x+dl[k],p.y+dc[k]});
                }
            }
        }
    }
    return 0;
}

int main()
{
    fin>>N>>M;
    for(int i=1;i<=N;i++){
        for(int j=1;j<=M;j++){
            fin>>mat[i][j];
            if(mat[i][j]=='D'){
                viz[i][j]=true;
                dist[i][j]=0;
                q.push({i,j});
            }
            if(mat[i][j]=='I'){
                start.x=i;
                start.y=j;
            }
            if(mat[i][j]=='O'){
                finish.x=i;
                finish.y=j;
            }
        }
    }
    computeDistance();

    int st=0, dr=inf, mij;
    while(dr-st>1){
        mij=(st+dr)/2;
        if(verificare(mij))
            st=mij;
        else
            dr=mij;
    }

    if(st==0)
        fout<<-1;
    else
        fout<<st;

    fin.close();
    fout.close();
    return 0;

}