#include <iostream>
#include <queue>

#define NMax 1010
#define Inf 1000000000

using namespace std;

int N, M, Value[NMax][NMax], SX, SY, FX, FY, S=-1;
queue <int> QX, QY;
int XD[4]={-1, 0, 1, 0}, YD[4]={0, 1, 0, -1};
bool Vis[NMax][NMax];

void Read ()
{
    freopen ("barbar.in", "r", stdin);
    scanf ("%d %d\n", &N, &M);
    for (int i=1; i<=N; ++i)
    {
        for (int j=1; j<=M; ++j)
        {
            char C;
            scanf ("%c", &C);
            if (C=='D')
            {
                Value[i][j]=1;
                QX.push (i);
                QY.push (j);
            }
            if (C=='*')
            {
                Value[i][j]=-1;
            }
            if (C=='I')
            {
                SX=i;
                SY=j;
            }
            if (C=='O')
            {
                FX=i;
                FY=j;
            }
        }
        scanf ("\n");
    }
    for (int i=0; i<=N+1; ++i)
    {
        Value[i][0]=Value[i][M+1]=-1;
    }
    for (int j=0; j<=M+1; ++j)
    {
        Value[0][j]=Value[N+1][j]=-1;
    }
}

void Print ()
{
    freopen ("barbar.out", "w", stdout);
    printf ("%d\n", S);
}

void BuildValue ()
{
    while (!QX.empty ())
    {
        int X=QX.front (); QX.pop ();
        int Y=QY.front (); QY.pop ();
        for (int d=0; d<4; ++d)
        {
            int NewX=X+XD[d];
            int NewY=Y+YD[d];
            if (Value[NewX][NewY]==0)
            {
                Value[NewX][NewY]=Value[X][Y]+1;
                QX.push (NewX);
                QY.push (NewY);
            }
        }
    }
}

bool Initialize (int DMax)
{
    if (Value[SX][SY]<DMax)
    {
        return false;
    }
    for (int i=1; i<=N; ++i)
    {
        for (int j=1; j<=M; ++j)
        {
            Vis[i][j]=false;
        }
    }
    while (!QX.empty ())
    {
        QX.pop ();
    }
    while (!QY.empty ())
    {
        QY.pop ();
    }
    Vis[SX][SY]=true;
    QX.push (SX);
    QY.push (SY);
    return true;
}

bool Lee (int DMax)
{
    if (!Initialize (DMax))
    {
        return false;
    }
    while (!QX.empty ())
    {
        int X=QX.front (); QX.pop ();
        int Y=QY.front (); QY.pop ();
        for (int d=0; d<4; ++d)
        {
            int NewX=X+XD[d];
            int NewY=Y+YD[d];
            if (Value[NewX][NewY]!=-1 and Value[NewX][NewY]>=DMax and !Vis[NewX][NewY])
            {
                Vis[NewX][NewY]=true;
                QX.push (NewX);
                QY.push (NewY);
                if (Vis[FX][FY])
                {
                    return true;
                }
            }
        }
    }
    if (Vis[FX][FY])
    {
        return true;
    }
    return false;
}

int main()
{
    Read ();
    BuildValue ();
    int L=1, R=Inf;
    while (L<=R)
    {
        int Mid=(L+R)/2;
        if (Lee (Mid))
        {
            S=Mid-1;
            L=Mid+1;
        }
        else
        {
            R=Mid-1;
        }
    }
    Print ();
    return 0;
}