#include <stdio.h>
#include <string.h>
#include <queue>
#include <vector>
#include <algorithm>

using namespace std;

const int START=2,FINISH=3,WALL=-1,EMPTY=0,DRAGON=1,INF=10000000;
int R,C,a[1004][1004],dist[1004][1004],GDist[1004][1004],viz[1004][1004];
char buff[1005];

class Point{
	public:int x,y,d;
	public:Point(int xx,int yy,int dd):x(xx),y(yy),d(dd){}
	public:bool operator<(Point other)const{return d<other.d;}
	public:bool operator>(Point other)const{return d>other.d;}
};

queue<Point> dragons;

bool isValid(int x,int y){
	return (x>=0 && x<R &&y>=0 && y<C && a[x][y]!=WALL && a[x][y]!=DRAGON);
}


Point startPoint=Point(0,0,0),endPoint=Point(0,0,0);
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};

bool isRoadDoable(int d){
	memset(viz,0,sizeof(viz));
	viz[startPoint.x][startPoint.y]=1;
	queue<Point> q;q.push(startPoint);
	while(!q.empty()){
		Point u = q.front();q.pop();
		for(int i=0;i<4;i++){
			if(isValid(u.x+dx[i],u.y+dy[i]) && !viz[u.x+dx[i]][u.y+dy[i]] && dist[u.x+dx[i]][u.y+dy[i]]>=d){
				viz[u.x+dx[i]][u.y+dy[i]]=true;
				q.push(Point(u.x+dx[i],u.y+dy[i],0));
			}
		}
	}
	return viz[endPoint.x][endPoint.y];
}


int main(){
	freopen("barbar.in","r",stdin);
	freopen("barbar.out","w",stdout);
	scanf("%d %d",&R,&C);
	for(int i=0;i<R;i++)
		for(int j=0;j<C;j++)
			dist[i][j]=INF;
			
	for(int i=0;i<R;i++){
		scanf("%s",buff);
		for(int j=0;j<C;j++){
			if(buff[j]=='.') a[i][j]=EMPTY;
			if(buff[j]=='*') a[i][j]=WALL;
			if(buff[j]=='D') {a[i][j]=DRAGON;dist[i][j]=0;dragons.push(Point(i,j,0));}
			if(buff[j]=='I') {a[i][j]=START;startPoint=Point(i,j,0);}
			if(buff[j]=='O') {a[i][j]=FINISH;endPoint=Point(i,j,0);}
		}
	}
	
	while(!dragons.empty()){
		Point dr=dragons.front();dragons.pop();
		
		for(int i=0;i<4;i++){
			if(isValid(dr.x+dx[i],dr.y+dy[i]) && dist[dr.x+dx[i]][dr.y+dy[i]]==INF){
				dist[dr.x+dx[i]][dr.y+dy[i]]=dist[dr.x][dr.y]+1;
				dragons.push(Point(dr.x+dx[i],dr.y+dy[i],0));
			}
		}
	}
	
	priority_queue<Point, vector<Point>, less<Point> > pq;
	
	
	/*
	startPoint.d=dist[startPoint.x][startPoint.y];
	GDist[startPoint.x][startPoint.y]=dist[startPoint.x][startPoint.y];
	viz[startPoint.x][startPoint.y]=1;
	pq.push(startPoint);
	while(!pq.empty()){
		Point u=pq.top();pq.pop();
		for(int i=0;i<4;i++){
			if(isValid(u.x+dx[i],u.y+dy[i]) && !viz[u.x+dx[i]][u.y+dy[i]]){
				viz[u.x+dx[i]][u.y+dy[i]]=true;
				GDist[u.x+dx[i]][u.y+dy[i]]=min(dist[u.x+dx[i]][u.y+dy[i]],u.d);
				pq.push(Point(u.x+dx[i],u.y+dy[i],GDist[u.x+dx[i]][u.y+dy[i]]));
			}
		}
	}
	if(viz[endPoint.x][endPoint.y])
		printf("%d",GDist[endPoint.x][endPoint.y]);
		else
		printf("-1");
	*/
	
	int maxD=-1;
	if(dist[startPoint.x][startPoint.y]!=INF){
		int st=1,dr=R*C;
		int mij;
		while(st<=dr){
			mij=(st+dr)>>1;
			if(isRoadDoable(mij)){
				maxD=mij;
				st=mij+1;
				
			}
			else{
				dr=mij-1;
			}
			
		}
	}
	printf("%d",maxD);
	
	return 0;		
}