#include<fstream>
#include<queue>
#include<cstring>
#include<vector>

#define punct pair<int,int>
#define x first
#define INF 0x3f3f3f3f
#define y second
#define mp make_pair
#define N 1010

using namespace std;

ifstream f("barbar.in");
ofstream g("barbar.out");

int i,j,n,m,li,ls,mij,sol,ok,xx,nxx,yy,nyy,dir;

int d[N][N],b[N][N];

bool a[N][N],viz[N][N];

vector<punct>v;
queue<punct>q;

punct pi,pf;

int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};

char s[1100];

inline bool ein(const int &x,const int &y){
    if(x < 1 || y < 1 || x > n || y > n)
        return 0;

    return 1;
}

inline bool verif(int dist)
{
    if(d[pi.x][pi.y] < dist)
        return 0;

    memset(viz, 0, sizeof(viz));
    while(!q.empty()) q.pop();

    q.push(pi);
    viz[pi.x][pi.y] = 1;

    while(!q.empty())
    {
        xx = q.front().x;
        yy = q.front().y;

        q.pop();

        for(int i = 0; i <= 3; ++i)
        {
            nxx = xx + dx[i];
            nyy = yy + dy[i];

            if(ein(nxx, nyy) && !a[nxx][nyy] && d[nxx][nyy] >= dist && !viz[nxx][nyy])
            {
                viz[nxx][nyy] = 1;
                q.push(make_pair(nxx, nyy));

                if(nxx == pf.x && nyy == pf.y)
                    return 1;
            }
        }
    }

    return 0;
}


int main()
{
    f >> n >> m;

    memset(d, INF, sizeof(d));

    for(i = 1; i <= n; ++i)
    {
        f >> (s + 1);

        for(j = 1; j <= m; ++j)
        {
            if(s[j] == '*')
                a[i][j] = 1;

            if(s[j] == 'I')
                pi.x = i,
                pi.y = j;

            if(s[j] == 'O')
                pf.x = i,
                pf.y = j;

            if(s[j] == 'D')
            {
                q.push(mp(i, j));
                d[i][j] = 0;
            }
        }
    }

    while(!q.empty())
    {
        xx = q.front().x;
        yy = q.front().y;

        q.pop();

        for(dir = 0; dir <= 3; ++dir)
        {
            nxx = xx + dx[dir];
            nyy = yy + dy[dir];

            if(ein(nxx, nyy) && !a[nxx][nyy] && d[xx][yy] + 1 < d[nxx][nyy])
            {
                d[nxx][nyy] = 1 + d[xx][yy];
                q.push(mp(nxx,nyy));
            }
        }
    }

    for(i = 1; i <= n; ++i)
        for(j = 1; j <= m; ++j)
            if(!a[i][j])
                ls = max(ls, d[i][j]);

    li = 0;
    sol = -1;

    while (li <= ls)
    {
        mij = (li + ls) >> 1;

        if(verif(mij))
            sol = mij, li = mij + 1;
        else
            ls = mij - 1;
    }

    g << sol << '\n';

    return 0;
}