#include <cstdio>
#include <queue>

#define in "barbar.in"
#define out "barbar.out"
#define NMAX (1000 + 7)

using namespace std;
int R, C, sol, px, py, lim, dirX[5] = {0, 1, 0, -1, 0}, dirY[5] = {0, 0, 1, 0, -1};
char mat[NMAX][NMAX], aux[NMAX][NMAX];
bool smth;
struct stare
{
    int x;
    int y;
    int p;
};
queue <stare> bfs;

void expand()
{
    stare tmp, newbie;
    while(!bfs.empty())
    {
        tmp = bfs.front();
        bfs.pop();
        if(tmp.p == lim) continue;
        for(int i = 1; i<= 4; ++i)
        {
            int p1 = tmp.x + dirX[i], p2 = tmp.y + dirY[i];
            if(aux[p1][p2] == 0 || aux[p1][p2] == 5)
            {
                aux[p1][p2] = -1;
                newbie.x = p1;
                newbie.y = p2;
                newbie.p = tmp.p + 1;
                bfs.push(newbie);
            }
            if(p1 == px && p2 == py)
            {
                smth = 1;
            }
        }
    }
}
bool way(const int &X, const int &Y)
{
    bool check = 0;
    for(int i = 1; i<= 4; ++i)
    {
        int p1 = X + dirX[i], p2 = Y + dirY[i];
        if(aux[p1][p2] == 0)
        {
            aux[p1][p2] = -1;
            if(way(p1, p2)) check = 1;
        }
        if(aux[p1][p2] == 5) return 1;
    }
    return check;
}
bool vef(const int &dist) /// nu e optim
{
    for(int i = 0; i<= R+1; ++i) aux[i][0] = aux[i][C+1] = -1;
    for(int i = 0; i<= C+1; ++i) aux[0][i] = aux[R+1][i] = -1;
    for(int i = 1; i<= R; ++i)
    {
        for(int j = 1; j<= C; ++j)
        {
            if(mat[i][j] == '.') aux[i][j] = 0;   ///liber
            if(mat[i][j] == '*') aux[i][j] = -1;  ///ocupat
            if(mat[i][j] == 'D') aux[i][j] = 1;   ///dragon
            if(mat[i][j] == 'I')
            {
                aux[i][j] = -1;
                px = i;
                py = j;
            }
            if(mat[i][j] == 'O') aux[i][j] = 5;   ///iesire
        }
    }
    smth = 0;
    lim = dist;
    stare tmp;
    tmp.p = 1;
    for(int i = 1; i<= R; ++i)
    {
        for(int j = 1; j<= C; ++j)
        {
            if(aux[i][j] == 1)
            {
                tmp.x = i;
                tmp.y = j;
                bfs.push(tmp);
            }
        }
    }
    expand();
    if(smth) return 0;
    /*for(int i = 1; i<= R; ++i)
    {
        for(int j = 1; j<= C; ++j)
        {
            if(i == px && j == py) {printf("P");continue;}
            if(aux[i][j] == -1) printf("X");
            else printf("%d", aux[i][j]);
        }
        printf("\n");
    }*/
    if(way(px, py)) return 1;
    return 0;
}

inline void citire()
{
    scanf("%d %d", &R, &C);
    for(int i = 1; i<= R; ++i)
    {
        scanf("%s", mat[i]+1);
    }
}
int cautbin()
{
    //printf("check enter\n");
    int start = 0, finish = R*C, step = 1;
    for( ; step <= finish; step<<=1);
    step >>= 1;
    for( ; step; step>>=1)
    {
        int index = start + step;
        //printf("check start = %d step = %d\n", start, step);
        if(index > finish) continue;
        if(vef(index)) start = index;
    }
    return start;
}

int main()
{
    freopen(in, "r", stdin);
    freopen(out, "w", stdout);
    citire();
    sol = cautbin();
    printf("%d\n", sol);
    return 0;
}