#include <bits/stdc++.h>

using namespace std;
ifstream fin("orase1.in");
ofstream fout("orase1.out");
long long INF=1e18;
int n,m,xSt,ySt,xFin,yFin;
char a[1005][1005];
int dist[1005][1005];
bool viz[1005][1005];
bool vizVerif[1005][1005];
queue<pair<int,int>> q;
int dx[]={0,1,0,-1};
int dy[]={-1,0,1,0};

void lee()
{
    while(!q.empty())
    {
        pair<int,int> curent=q.front();
        q.pop();
        for(int k=0;k<=3;k++)
        {
            int lin=curent.first+dx[k];
            int col=curent.second+dy[k];
            if(lin>=1 and lin<=n and col>=1 and col<=m and viz[lin][col]==0)
            {
                viz[lin][col]=1;
                dist[lin][col]=dist[curent.first][curent.second]+1;
                q.push({lin,col});
            }
        }

    }
}

bool verificare(int d)
{
    queue<pair<int,int>> coada;
    vizVerif[xSt][ySt]=1;
    coada.push({xSt,ySt});
    while(!coada.empty())
    {
        pair<int,int> curent=coada.front();
        coada.pop();
        for(int k=0;k<=3;k++)
        {
            int lin=curent.first+dx[k];
            int col=curent.second+dy[k];
            if(lin>=1 and lin<=n and col>=1 and col<=m and vizVerif[lin][col]==0 and dist[lin][col]>=d)
            {
                coada.push({lin,col});
                vizVerif[lin][col]=1;
                if(lin==xFin and col==yFin)return true;
            }

        }
    }
    return false;

}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    fin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            fin>>a[i][j];
            if(a[i][j]=='*')viz[i][j]=1;
            else if(a[i][j]=='I')
            {
                xSt=i;
                ySt=j;
            }
            else if(a[i][j]=='O')
            {
                xFin=i;
                yFin=j;
            }
            else if(a[i][j]=='D')
            {
                q.push({i,j});
                viz[i][j]=1;
            }
        }
    }


    lee();
    int st=0, dr=1000*1000,rasp=0;
    while(st<=dr)
    {
        int mij=(st+dr)/2;
        if(verificare(mij))
        {
            rasp=mij;
            st=mij+1;
        }
        else
        {
            dr=mij-1;
        }

    }
    fout<<rasp;



    return 0;
}