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

using namespace std;

char a[1001][1001];
int m,n;
int dist[1001][1001];
int x0,y0,xf,yf;

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

vector< pair<int,int> > dragoni;

typedef struct{int x,y,dist;} nod;

bool operator<(nod x, nod y){
    return x.dist>y.dist;
}


bool viz[1001][1001];
int dirx[4] = {-1,0,+1,0};
int diry[4] = {0,+1,0,-1};
void dijkstra(){
	priority_queue< nod > q;
	nod x,y;
	for (std::vector< pair<int,int> >::iterator i = dragoni.begin(); i != dragoni.end(); ++i)
	{
			x.x = i->first; x.y = i->second; x.dist = 0;
			q.push(x);
	}

	do{
		x=q.top();
		q.pop();
		if(!viz[x.x][x.y]){
			viz[x.x][x.y] = true; dist[x.x][x.y] = x.dist;
			for (int i = 0; i < 4; ++i)
			{
				y.x = x.x + dirx[i]; y.y = x.y + diry[i];
				if(y.x >= 0 && y.x<m && y.y>=0 && y.y<n) 
					if(!viz[y.x][y.y]){
						y.dist = x.dist + 1;
						q.push(y);
					}
			}
		}


	}while(!q.empty());
}

int solve(){
	queue< pair<int,int> > q;
	vector< pair<int,int> > v;
	int step = dist[x0][y0];
	bool finished = false;
	v.push_back(make_pair(x0,y0));
	pair<int,int> cur,nod;
	for (int i = 0; i < m; ++i)
		{
			for (int j = 0; j < n; ++j)
			{
				viz[i][j] = false;
			}
		}
	viz[x0][y0] = true;
	while(!finished && step>0){
		for (int it = 0; it<v.size(); ++it)
		{
			cur = v[it];
			// cout<<cur.first<<' '<<cur.second<<'\n';
			for (int i = 0; i < 4; ++i)
			{
				nod.first = cur.first + dirx[i];
				nod.second = cur.second + diry[i];
				if(nod.first >= 0 && nod.first<m && nod.second>=0 && nod.second<n){
					if(!viz[nod.first][nod.second])
						if(dist[nod.first][nod.second] >= step){
						v.push_back(nod);
						
						// cout<<cur.first<<' '<<cur.second<<" => "<<nod.first<<" "<<nod.second<<"\n";
						// for (std::vector< pair<int,int> >::iterator itx = v.begin(); itx != v.end(); ++itx)
						// 	{
						// 		cout<<itx->first<<' '<<itx->second<<", ";
						// 	}
						// cout<<"\n";

						viz[nod.first][nod.second] = true;
						if(nod.first == xf && nod.second == yf){
							return step;
						}
					}				
				} 
			}
		}
	step--;
	}

	return -1;
}


int main(int argc, char const *argv[])
{
	fin>>m>>n;
	for (int i = 0; i < m; ++i)
		{
			for (int j = 0; j < n; ++j)
			{
				fin>>a[i][j];
				if(a[i][j]=='D') dragoni.push_back(make_pair(i,j));
				dist[i][j]=1<<20;
				if(a[i][j]=='I'){
					x0 = i; y0 = j;
				}
				if(a[i][j]=='O'){
					xf = i; yf = j;
				}
			}
		}	


			dijkstra();
			// for (int i = 0; i < m; ++i)
			// {
			// 	for (int j = 0; j < n; ++j)
			// 	{
			// 		fout<<dist[i][j];
			// 	}
			// 	fout<<'\n';
			// }

			fout<<solve();

	return 0;
}