#include <stdio.h>
#define SI 1000000 
#define Nmax 1011
int b[Nmax][Nmax];
int a[Nmax][Nmax];
struct punct{int c1,c2;};
punct plec,sos;
short int va[Nmax*Nmax];
short int vb[Nmax*Nmax];
int nrv;
const int lin[]={0,1,0,-1};
const int col[]={1,0,-1,0};

int rez,R,C;
inline int minim(int x,int y)
{
	if(x<y)
		return x;
	return y;
}	
void read()
{
	char ch;
	freopen("barbar.in", "r",stdin);
	freopen("barbar.out", "w",stdout);
	scanf("%d%d", &R,&C);
	for(int i=1;i<=R;++i)
	{
		scanf("%c", &ch);
		for(int j=1;j<=C;++j)
		{
			scanf("%c", &ch);
			a[i][j]=SI;
			if(ch=='I')
			{
				plec.c1=i;
				plec.c2=j;
			}	
			if(ch=='O')
			{
				sos.c1=i;
				sos.c2=j;
			}	
			if(ch=='*')
				a[i][j]=-1;
			if(ch=='D')
			{
				a[i][j]=0;
				va[++nrv]=i;
				vb[nrv]=j;
			}
		}	
	}	
}
void lee(int x,int y)
{
	for(int t=0;t<4;t++)
		if((a[x+lin[t]][y+col[t]]>a[x][y]+1))
		{
			a[x+lin[t]][y+col[t]]=a[x][y]+1;
			va[++nrv]=x+lin[t];
			vb[nrv]=y+col[t];
		}
}	
inline int ok(int xx,int yy)
{
	if(xx<=R && xx>=1 && yy<=C && yy>=1)
		return 1;
	return 0;
}	
/*void fill(int x,int y,int dist)
{
	for(int t=0;t<4;t++)
		if(a[x+lin[t]][y+col[t]]>=z && a[x+lin[t]][y+col[t]]!=-1 && ok(x+lin[t],y+col[t]) && b[x+lin[t]][y+col[t]]!=dist)
		{
			b[x+lin[t]][y+col[t]]=dist;
			va[++nrv]=x+lin[t];
			vb[nrv]=y+col[t];
		}
}*/
inline int verifica(int dist)
{
	int p=1,x,y; 
	nrv=1;
	va[1]=plec.c1; 
	vb[1]=plec.c2; 
	if(!dist) 
		for(int i=1;i<=R;++i) 
			for(int j=1;j<=C;++j) 
				b[i][j]=1; 
	while(p<=nrv) 
	{ 
		for(int i=0;i<4;i++)
		{ 
			x=va[p]+lin[i]; 
			y=vb[p]+col[i]; 
			if(a[x][y]>=dist && b[x][y]!=dist) 
			{
				if(x==sos.c1 && y==sos.c2) 
					return 1;
				va[++nrv]=x; 
				vb[nrv]=y; 
				b[x][y]=dist; 
			} 
		} 
		++p; 
	} 
	/*for(int i=1;i<=R;++i)
	{
		printf("\n");
		for(int j=1;j<=C;++j)
			printf("%d ",b[i][j]);
	}
	printf("\n");*/	
	return 0; 
}	
void make_lee()
{
	for(int i=1;i<=nrv;i++)
		lee(va[i],vb[i]);
	//int m,u=0,p=1000000;
	/*while(u<=p)
	{
		m=(u+p)/2;
		if(verifica(m) )
			if(!verifica(m+1))
			{
				printf("%d\n",m);
				return;
			}
			else
				u=m+1;
		else
			p=m-1;
	}*/
	for(int k=100000;k>=1;--k)
		if(verifica(k) )
		{
			printf("%d\n", k);
			return;
		}	
	printf("-1");
}
int main()
{
	read();
	make_lee();
	return 0;
}