#include <fstream>
#include <iostream>
#include <queue>

using namespace std;

ifstream fi("barbar.in");
ofstream fo("barbar.out");

void fill(int x, int y, int cost);
bool check(int k);
int caut();
void bordare();
void citeste();
void fazero();
bool existasol();

int dl[] = { -1, 0, 1, 0 };
int dc[] = { 0, 1, 0, -1 };

struct coada{

	int lin, col;
};

queue<coada> C;

int mat[1004][1004], c[1004][1004];

int n, m, start = 1, ultim = 1;
int pl, pc, cl, cc;


int main()
{
	int x, y, xx, yy, dist;
	coada b;
	citeste();
	bordare();
	if (existasol())
	{
		fazero();
		while (!C.empty())
		{
			x = C.front().lin;
			y = C.front().col;
			for (int i = 0; i < 4; i++)
			{
				xx = x + dl[i];
				yy = y + dc[i];
				if (mat[xx][yy] == 0)
				{
					b.lin = xx;
					b.col = yy;
					C.push(b);
					mat[xx][yy] = mat[x][y] + 1;
				}
			}
			C.pop();
		}
		dist = caut();
		fo << dist;
	}
	else fo << -1;
	return 0;
}
void citeste()
{
	int i, j;
	char a;
	coada b;
	fi >> n >> m;
	for (i = 1; i <= n; i++)
	{
		for (j = 1; j <= m; j++)
		{
			fi >> a;
			if (a == '.')
				mat[i][j] = 0;
			if (a == 'D')
			{
				mat[i][j] = 0;
				c[i][j] = -1;
				b.lin = i;
				b.col = j;
				C.push(b);
			}
			if (a == 'I')
			{
				pl = i;
				pc = j;
			}
			if (a == 'O')
			{
				cl = i;
				cc = j;
			}
			if (a == '*')
			{
				mat[i][j] = -1;
				c[i][j] = -1;
			}
		}
	}
}
void bordare()
{
	int i, j;
	for (i = 0; i <= n + 1; i++)
	{
		mat[i][0] = -1;
		mat[i][m + 1] = -1;
		c[i][0] = -1;
		c[i][m + 1] = -1;
	}
	for (j = 0; j <= m + 1; j++)
	{
		mat[0][j] = -1;
		mat[n + 1][j] = -1;
		c[0][j] = -1;
		c[n + 1][j] = -1;
	}
}
bool check(int k)
{
	c[cl][cc] = 0;
	fill(pl, pc, k);
	if (c[cl][cc] >= k)
		return true;
	return false;
}
int caut()
{
	int i = 0;
	int pas = 1 << 10;
	while (pas)
	{
		if (check(i + pas))
			i += pas;
		pas /= 2;
		fazero();
	}
	return i;
}
void fill(int x, int y, int cost)
{
	int i;
	int xx, yy;
	c[x][y] = cost;
	for (i = 0; i < 4; i++)
	{
		xx = x + dl[i];
		yy = y + dc[i];
		if (mat[xx][yy] >= cost && c[xx][yy]==0)
			fill(xx, yy, cost);
	}
}
void fill1(int x, int y, int cost)
{
	int i;
	int xx, yy;
	c[x][y] = cost;
	for (i = 0; i < 4; i++)
	{
		xx = x + dl[i];
		yy = y + dc[i];
		if (c[xx][yy] == 0)
			fill1(xx, yy, cost);
	}
}
void fazero()
{
	int i, j;
	for (i = 1; i <= n; i++)
	{
		for (j = 1; j <= n; j++)
			c[i][j] = 0;
	}
}
bool existasol()
{
	c[pl][pc] = 0;
	fill1(pl, pc, 1);
	if (c[cl][cc] != 0)
		return true;
	return false;
}