#include <iostream>
#include <fstream>
#include <stdio.h>

using namespace std;

#define MAX 1010

void ver(char m[MAX][MAX], char check[MAX][MAX], int R, int C, int x, int y);

void peretificare(char m[MAX][MAX], int R, int C, int dist);

int main()
{
    ifstream fin("barbar.in");
    ofstream fout("barbar.out");

    int R, C, dist, i_start, j_start, i_iesire, j_iesire;
    char m[MAX][MAX], check[MAX][MAX] = {0};

    fin >> R >> C;

    for (int i = 0; i < R; i++) {
        for (int j = 0; j < C; j++) {
            fin >> m[i][j];

            if (m[i][j] == 'I') {
                i_start = i;
                j_start = j;

                m[i][j] = '.';
            } else if (m[i][j] == 'O') {
                i_iesire = i;
                j_iesire = j;

                m[i][j] = '.';
            }
        }
    }

    check[i_start][j_start] = 1;

    ver(m, check, R, C, i_start, j_start);

    if (check[i_iesire][j_iesire] == 0) {
        fout << -1;

        return 0;
    }

    for (dist = 1; dist < MAX; dist++) {
        peretificare(m, R, C, dist);

        for (int i = 0; i < R; i++) {
            for (int j = 0; j < C; j++) {
                check[i][j] = 0;
            }
        }

        if (m[i_start][j_start] != '*') {
            check[i_start][j_start] = 1;
        } else {
            break;
        }

        ver(m, check, R, C, i_start, j_start);

        if (check[i_iesire][j_iesire] != 1) {
            break;
        }
    }

    fout << dist;

    fin.close();
    fout.close();
    return 0;
}

void ver(char m[MAX][MAX], char check[MAX][MAX], int R, int C, int x, int y) {
    int newx, newy;

    if (x < C - 1) {
        newx = x + 1;
        newy = y;

        if (check[newx][newy] == 0) {
            if (m[newx][newy] == 'D' || m[newx][newy] == '*') {
                check[newx][newy] = 2;
            } else {
                check[newx][newy] = 1;
                ver(m, check, R, C, newx, newy);
            }
        }
    }

    if (y < R - 1) {
        newx = x;
        newy = y + 1;

        if (check[newx][newy] == 0) {
            if (m[newx][newy] == 'D' || m[newx][newy] == '*') {
                check[newx][newy] = 2;
            } else {
                check[newx][newy] = 1;
                ver(m, check, R, C, newx, newy);
            }
        }
    }

    if (x >= 1) {
        newx = x - 1;
        newy = y;

        if (check[newx][newy] == 0) {
            if (m[newx][newy] == 'D' || m[newx][newy] == '*') {
                check[newx][newy] = 2;
            } else {
                check[newx][newy] = 1;
                ver(m, check, R, C, newx, newy);
            }
        }
    }

    if (y >= 1) {
        newx = x;
        newy = y - 1;

        if (check[newx][newy] == 0) {
            if (m[newx][newy] == 'D' || m[newx][newy] == '*') {
                check[newx][newy] = 2;
            } else {
                check[newx][newy] = 1;
                ver(m, check, R, C, newx, newy);
            }
        }
    }
}

void peretificare(char m[MAX][MAX], int R, int C, int dist) {
    for (int i = 0; i < R; i++) {
        for(int j = 0; j < C; j++) {
            if (m[i][j] == 'D') {
                int ki = i - dist, kj = j;

                while (ki < i) {
                    if (ki >= 0 && kj <= C - 1 && m[ki][kj] == '.') {
                        m[ki][kj] = '*';
                    }

                    ki++;
                    kj++;
                }

                while (kj > j) {
                    if (ki <= R - 1 && kj <= C - 1 && m[ki][kj] == '.') {
                        m[ki][kj] = '*';
                    }

                    ki++;
                    kj--;
                }

                while (ki > i) {
                    if (ki <= R - 1 && kj >= 0 && m[ki][kj] == '.') {
                        m[ki][kj] = '*';
                    }

                    ki--;
                    kj--;
                }

                while (kj < j) {
                    if (ki >= 0 && kj >= 0 && m[ki][kj] == '.') {
                        m[ki][kj] = '*';
                    }

                    ki--;
                    kj++;
                }
            }
        }
    }
}