#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define fs first
#define sc second
#define rep(i, from, to) for (int i = from; i < (to); ++i)
#define all(x) x.begin(), x.end()
#define sz(x) (int) (x).size()
#define FOR(i, to) for (int i = 0; i < (to); ++i)

using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef pair<double,double> pdd;
typedef vector<ll> vll;
typedef vector<pair<int,int> > vpi;
typedef pair<ll,ll> pll;
typedef vector<string> vs;
#define MOD 1000000007
#define INF 1000000000LL * 100000000LL
#define Nmax 202020
int T;

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

int D[1020][1020];
int B[1020][1020];
string s[2222];
int mmax = 0;
int N,M;
queue<pii> Q;
int xI, yI, xO, yO;

int isB(int x,int y)
{
    if(x < 0 || y < 0 || x >= N || y >= M || s[x][y] == '*') return 1;
    return 0;
}

void do_dragons()
{
    while(!Q.empty())
    {
        pii a = Q.front(); Q.pop();
        FOR(k, 4)
        {
            if(isB(a.fs + dx[k], a.sc + dy[k])) continue;
            if(D[a.fs + dx[k]][a.sc + dy[k]] == 0)
            {
                D[a.fs + dx[k]][a.sc + dy[k]] = D[a.fs][a.sc] + 1;
                Q.push(mp(a.fs + dx[k], a.sc+dy[k]));
            }
        }
    }
}

int isok(int val)
{
    Q.push(mp(xI, yI));
    while(!Q.empty())
    {
        pii a = Q.front(); Q.pop();
        FOR(k, 4)
        {
            if(isB(a.fs + dx[k], a.sc + dy[k])) continue;
            if(D[a.fs + dx[k]][a.sc + dy[k]] < val) continue;
            if(B[a.fs + dx[k]][a.sc + dy[k]] != val)
            {
                B[a.fs + dx[k]][a.sc + dy[k]] = val;
                Q.push(mp(a.fs + dx[k], a.sc+dy[k]));
            }
        }
    }
    return B[xO][yO] == val;
}

int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    cin >> N >> M;
    FOR(i, N)
    {
        cin >> s[i];
    }
    FOR(i, N)
    {
        FOR(j, M)
        {
            if(s[i][j] == 'D')
            {
                D[i][j] = 1;
                Q.push(mp(i,j));
            }
            else
                if (s[i][j] == 'I')
                {
                    xI = i; yI = j;
                }
                else
                    if (s[i][j] == 'O')
                    {
                        xO = i; yO = j;
                    }
        }
    }
    do_dragons();
    int ret = 0;
    int st = D[xI][yI];
    int dr = 0;
    FOR(i, N) FOR(j, M)
        dr = max(dr, D[i][j]);
    while(st <= dr)
    {
        int mij = (st+dr)/2;
        if(isok(mij))
        {
            ret = mij;
            st = mij + 1;
        }
        else
            {
                dr = mij - 1;
            }
    }
    cout << ret - 1 << endl;
}