#include <fstream>
#include <queue>

using namespace std;

ifstream in;
ofstream out;

char ti[1005][1005], t[1005][1005]; bool aux[1005][1005];
int n, m;

pair<int, int> dir[] = { {-1,0},{1,0},{0,-1},{0,1} };

void set(char setme[1005][1005], char to[1005][1005])
{
	for (int i = 0; i < 1005; i++)
	{
		for (int j = 0; j < 1005; j++)
		{
			setme[i][j] = to[i][j];
		}
	}
}

void set(bool setme[1005][1005], bool to)
{
	for (int i = 0; i < 1005; i++)
	{
		for (int j = 0; j < 1005; j++)
		{
			setme[i][j] = to;
		}
	}
}

bool isInside(int l, int c)
{
	return l >= 0 && c >= 0 && l < n && c < m;
}

bool isInside(pair<int,int> x)
{
	return x.first >= 0 && x.second >= 0 && x.first < n && x.second < m;
}

void expand(int amount)
{
	set(aux, 0);
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			if (t[i][j] == 'D')
			{
				for (int l = i - amount; l <= i + amount; l++)
				{
					for (int c = j - amount + abs(i - l); c <= j + amount - abs(i - l); c++)
					{
						if (isInside(l, c))
						{
							aux[l][c] = 1;
						}
					}
				}
			}
		}
	}
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			if (aux[i][j] == 1)
				t[i][j] = 'F';
		}
	}
}

pair<int, int> plu(pair<int, int> a, pair<int, int> b)
{
	return { a.first + b.first, a.second + b.second };
}

bool canfindway(int startx, int starty)
{
	/*for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			out << t[i][j];
		}
		out << "\n";
	}
	out << "\n\n";*/
	set(aux, 0);
	queue<pair<int, int>> q;
	aux[startx][starty] = 1;
	q.push({ startx, starty });
	while (!q.empty())
	{
		auto x = q.front();
		for (int i = 0; i < 4; i++)
		{
			auto c = plu(x, dir[i]);
			if (isInside(c) && !aux[c.first][c.second])
			{
				if (t[c.first][c.second] == 'O')
					return 1;
				else if (t[c.first][c.second] == '.')
				{
					aux[c.first][c.second] = 1;
					q.push(c);
				}
			}
		}
		q.pop();
	}
	return 0;
}

int main()
{
	in.open("barbar.in");
	out.open("barbar.out");
	in >> n >> m;
	int startx, starty;
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			in >> ti[i][j];
			if (ti[i][j] == 'I')
			{
				startx = i;
				starty = j;
			}
		}
	}
	int st = 0, dr = max(n,m)*2, mij, r = -1;
	while (st <= dr)
	{
		mij = (st + dr) / 2;
		set(t, ti);
		expand(mij);
		if (canfindway(startx, starty) && t[startx][starty] == 'I')
		{
			r = mij;
			st = mij + 1;
		}
		else
			dr = mij - 1;
	}
	out << r+1;
}