#include <fstream>
#include <cstring>
#include <queue>
#define In "barbar.in"
#define Out "barbar.out"
#define Nmax 1002
#define Inf 0x3f3f3f3f
#define lin first
#define col second
using namespace std;
char a[Nmax][Nmax];
int dist[Nmax][Nmax],n,m,sol;
bool viz[Nmax][Nmax];
queue< pair<int ,int > >Q;
pair<int ,int >pp,ps;
int dl[]={ 0, 1,-1, 0};
int dc[]={ 1, 0, 0,-1};
inline void Citire()
{
    ifstream f(In);
    f>>n>>m;
    for(int i=1;i<=n;i++)
        f>>(a[i]+1);
    f.close();
}
inline void Bordare()
{
    int i;
    for(i=1;i<=n;i++)
        a[i][0] = a[i][m+1] = '*';
    for(i=1;i<=m;i++)
        a[0][i] = a[n+1][i] = '*';
}
inline void Init()
{
    int i,j;
    memset(dist,Inf,sizeof(dist));
    Bordare();
    for(i=1;i<=n;i++)
        for(j=1;j<=m;j++)
            if(a[i][j]=='D')
            {
                Q.push(make_pair(i,j));
                dist[i][j] = 0;
            }
            else
                if(a[i][j]=='I')
                {
                    pp.lin = i;
                    pp.col = j;
                }
                else
                    if(a[i][j]=='O')
                    {
                        ps.lin = i;
                        ps.col = j;
                    }
}
inline void CalculDist()
{
    pair<int ,int >p,v;
    int i;
    while(!Q.empty())
    {
        p = Q.front();
        Q.pop();
        for(i=0;i<4;i++)
        {
            v.lin = p.lin + dl[i];
            v.col = p.col + dc[i];
            if(a[v.lin][v.col]!='*' && dist[v.lin][v.col]>dist[p.lin][p.col]+1)
            {
                dist[v.lin][v.col] = dist[p.lin][p.col]+1;
                Q.push(v);
            }
        }
    }
}

//returneaza 1 daca exista un traseu care sa nu treca prin elemente <lim
inline bool Compatibil(int lim)
{
    if(dist[pp.lin][pp.col]<lim)
        return false;
    memset(viz,0,sizeof(viz));
    viz[pp.lin][pp.col] = true;
    pair< int ,int > p,v;
    while(!Q.empty())
        Q.pop();
    Q.push(pp);
    while(!Q.empty())
    {
        p = Q.front();
        Q.pop();
        for(int i=0;i<4;i++)
        {
            v.lin = p.lin + dl[i];
            v.col = p.col + dc[i];
            if(a[v.lin][v.col]!='*' && viz[v.lin][v.col]==false && dist[v.lin][v.col]>=lim)
            {
                if(v.lin==ps.lin && v.col==ps.col)
                    return true;
                Q.push(v);
                viz[v.lin][v.col] = true;
            }
        }
    }
    return false;
}
inline void Rezolvare()
{
    Init();
    CalculDist();
    int st,dr,mijl;
    st = 0;
    dr = n+m;
    while(st<=dr)
    {
        mijl = (st+dr)>>1;
        if(Compatibil(mijl))
        {
            sol = mijl;
            st = mijl+1;
        }
        else
            dr = mijl-1;
    }
    ofstream g(Out);
    g<<sol<<"\n";
    g.close();
}
int main()
{
    Citire();
    Rezolvare();
    return 0;
}