#include <fstream>
#include <bitset>
#include <queue>
#define inf 2001
using namespace std;
ifstream fin ("barbar.in");
ofstream fout ("barbar.out");
bitset <1001> viz[1001],zid[1001][1001];
struct el
{
    short int i,j;
};
queue <el> q;
char ch;
short int d,lv,cv,dx[]={0,1,-1,0,0},dy[]={0,0,0,1,-1};
short int l,c,xi,xf,yi,yf,n,m,i,j,st,mij,dr,dp[1001][1001];
bool f (short int val)
{
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
            viz[i][j]=0;
    }
    if (dp[xi][yi]<val)
        return 0;
    viz[xi][yi]=1;
    q.push ({xi,yi});
    while (!q.empty ())
    {
        l=q.front ().i;
        c=q.front ().j;
        q.pop ();
        for (d=1; d<=4; d++)
        {
            lv=l+dx[d];
            cv=c+dy[d];
            if (lv>0&&lv<=n&&cv>0&&cv<=m&&dp[lv][cv]>=val&&viz[lv][cv]==0&&zid[lv][cv]==0)
            {
                viz[lv][cv]=1;
                q.push ({lv,cv});
            }
        }
    }
    return viz[xf][yf];
}
int main()
{
    fin>>n>>m;
    for (i=1; i<=n; i++)
    {
        for (j=1; j<=m; j++)
        {
            dp[i][j]=inf;
            fin>>ch;
            if (ch=='*')
                zid[i][j]=1;
            else if (ch=='D')
            {
                q.push ({i,j});
                dp[i][j]=0;
            }
            else if (ch=='I')
            {
                xi=i;
                yi=j;
            }
            else if (ch=='O')
            {
                xf=i;
                yf=j;
            }
        }
    }
    while (!q.empty ())
    {
        l=q.front ().i;
        c=q.front ().j;
        q.pop ();
        for (d=1; d<=4; d++)
        {
            lv=l+dx[d];
            cv=c+dy[d];
            if (lv>0&&lv<=n&&cv>0&&cv<=m&&dp[lv][cv]>dp[l][c]+1&&zid[lv][cv]==0)
            {
                dp[lv][cv]=dp[l][c]+1;
                q.push ({lv,cv});
            }
        }
    }
    st=1;
    dr=n+m;
    while (st<=dr)
    {
        mij=(st+dr)/2;
        if (f (mij)==1)
            st=mij+1;
        else
            dr=mij-1;
    }
    if (dr==0)
        dr--;
    fout<<dr;
    return 0;
}