#include <cstdio>
#include <queue>
#include <algorithm>

using namespace std;

const int nmax=1005;

char a[nmax][nmax];
int d[nmax][nmax];
bool viz[nmax][nmax];

int vmax;
int r, c;

pair <int, int> start;
pair <int, int> finish;

queue < pair<int, int> > drag;

int x[]={-1, 0, 1, 0}, y[]={0, 1, 0, -1};

inline bool verif(int i, int j)
{
	return i>=0 && j>=0 && i<r && j<c;
}

void bfs()
{
	while(!drag.empty())
	{
		pair <int, int> temp=drag.front();
		for(int i=0;i<4;i++)
		{
			pair <int, int> current(temp.first+x[i], temp.second+y[i]);
			int u=temp.first+x[i];
			int v=temp.second+y[i];
			if(verif(u, v) && a[u][v]!='*' && d[u][v]==0)
			{
				drag.push(current);
				d[u][v]=d[temp.first][temp.second]+1;
				vmax=max(vmax, d[u][v]);
			}
		}
		drag.pop();
	}
}
void bfss()
{
	queue <pair <int, int> > t;
	queue <pair <int, int> > q;

	t.push(start);

	while(!t.empty() && vmax>=0)
	{
		while(!t.empty())
		{
			q.push(t.front());
			t.pop();
		}

		while(!q.empty())
		{
			pair <int, int> temp=q.front();
			bool ok;

			for(int i=0;i<4;i++)
			{
				ok=true;

				pair <int, int> current(temp.first+x[i], temp.second+y[i]);
				int u=temp.first+x[i];
				int v=temp.second+y[i];

				if(verif(u, v) && a[u][v]!='*' && (!viz[u][v]) && d[u][v]>=vmax)
				{
					viz[u][v]=1;
					ok=false;
					q.push(current);
				}
			}
			q.pop();

			if(ok) t.push(temp);
		}

		if(viz[finish.first][finish.second]==1)return ;

		if(!t.empty()) vmax--;
	}
}

int main()
{
    freopen("barbar.in", "r", stdin);
    freopen("barbar.out", "w", stdout);

    scanf("%d%d", &r, &c);
    scanf("\n");
    for(int i=0;i<r;i++)
	{
		for(int j=0;j<c;j++)
		{
			scanf("%c", &a[i][j]);
			if(a[i][j]=='D')
				drag.push(pair <int, int> (i, j));
			if(a[i][j]=='I')
				start=pair <int, int> (i, j);
			if(a[i][j]=='O')
				finish=pair <int, int> (i, j);
		}
		scanf("\n");
	}

	bfs();
	bfss();

	printf("%d\n", min(vmax, d[start.first][start.second]));
    return 0;
}