#include <fstream>
#include <queue>
#include <climits>

using namespace std;

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

struct pos
{
	int x, y;
	int pas;
};

int n, m;
int maxx = INT_MIN;
int mat[1005][1005];
int d[4][2] = { {0, 1}, {1, 0}, {-1, 0}, {0, -1} };
int viz[1005][1005];
queue<pos> dragoni;
pos start, finish;
bool found = 0;

void leeDragoni()
{
	while (!dragoni.empty())
	{
		for (int i = 0; i <= 3; i++)
		{
			int nx = dragoni.front().x + d[i][0], ny = dragoni.front().y + d[i][1];
			if (nx < 1 || ny < 1 || nx > n || ny > m) continue;
			if (mat[nx][ny] != 0) continue;
			mat[nx][ny] = dragoni.front().pas - 1;
			dragoni.push({nx, ny, dragoni.front().pas - 1});
		}
		dragoni.pop();
	}
}

class Compare {
public:
	bool operator()(pos a, pos b) {
		if (a.pas > b.pas) {
			return true;
		}
		return false;
	}
};

priority_queue<pos, vector<pos>, Compare> q;

void priorityLee()
{
	start.pas = mat[start.x][start.y];
	q.push(start);
	viz[start.x][start.y] = 1;
	while (!q.empty())
	{
		int x = q.top().x;
		int y = q.top().y;
		int val = q.top().pas;
		if (val > maxx)
		{
			maxx = val;
		}
		if (x == finish.x && y == finish.y)
		{
			found = 1;
			break;
		}
		q.pop();
		for (int i = 0; i <= 3; i++)
		{
			int nx = x + d[i][0], ny = y + d[i][1];
			if (nx < 1 || ny < 1 || nx > n || ny > m) continue;
			if (mat[nx][ny] >= 0 || viz[nx][ny] == 1) continue;
			viz[nx][ny] = 1;
			pos next;
			next.x = nx;
			next.y = ny;
			next.pas = mat[nx][ny];
			q.push(next);
		}
	}
}

int main()
{
	fin >> n >> m;
	char x;
	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= m; j++)
		{
			fin >> x;
			if (x == '.')
			{
				mat[i][j] = 0;
			}
			else if (x == 'I')
			{
				mat[i][j] = 0;
				start.x = i;
				start.y = j;
			}
			else if (x == 'O')
			{
				mat[i][j] = 0;
				finish.x = i;
				finish.y = j;
			}
			else if (x == 'D')
			{
				mat[i][j] = 4;
				dragoni.push({ i, j, 0 });
			}
			else
			{
				mat[i][j] = 1;
			}
		}
	}
	leeDragoni();
	priorityLee();
	if (found)
	{
		fout << -maxx;
	}
	else
	{
		fout << -1;
	}
}