#include <cstdio> 
#include <cstring> 
#include <algorithm> 
using namespace std; 

#define mp make_pair 
#define x first 
#define y second 

const int dx[] = {0, 1, 0, -1}; 
const int dy[] = {1, 0, -1, 0}; 

 
const int MAX_N = 1001; 
const int INF = 0x3f3f3f3f;

int n, m, k; 
char s[MAX_N][MAX_N]; 
int d[MAX_N][MAX_N], f[MAX_N][MAX_N]; 
pair <int, int> q[MAX_N * MAX_N * 2], O; 
 
 
void getDistance() 

{ 
    
int i, j; 

 for (i = 1; i <= k; ++i) 
    
{ for (j = 0; j < 4; ++j) 
	{ int newx = q[i].x + dx[j]; 
		int newy = q[i].y + dy[j];  
if (0 <= newx && newx < n && 0 <= newy && newy < m && s[newx][newy] != '*' && d[q[i].x][q[i].y] + 1 < d[newx][newy])             
	{d[newx][newy] = d[q[i].x][q[i].y] + 1;                 
     q[++k] = mp(newx, newy);            
	} 
      
		}   
	} 
} 

int check(int X) {  int i, j; 
						k = 0; 
  
		memset(f, 0, sizeof(f));  
for (i = 0; i < n && !k; ++i)         
	for (j = 0; j < m; ++j) 
            
		if (s[i][j] == 'I') 
            
{ 
	q[++k] = mp(i, j);                 
		break;             
} 
f[q[1].x][q[1].y] = 1;  
	 for (i = 1; i <= k; ++i)     
	{         
		for (j = 0; j < 4; ++j) 
        
		{ 
			int newx = q[i].x + dx[j]; 
        
			int newy = q[i].y + dy[j];  
 
	if (0 <= newx && newx < n && 0 <= newy && newy < m && s[newx][newy] != '*' && s[newx][newy] != 'D' && d[newx][newy] >= X && !f[newx][newy])             
{ 
               
		q[++k] = mp(newx, newy);           
	f[newx][newy] = 1; 
                 
		if (newx == O.x && newy == O.y)                     
return 1; 
            
		} 
			
	}     
} 
	
return 0; } 
void binSearch() 
{   
	int l = 0, r = n + m, mij, ret = 0, ok = 0;  
   while (l < r)   
	{ 
mij = (l + r) >> 1; 
		if (check(mij))          
	ret = mij, l = mij + 1, ok = 1; 
		else            
	r = mij - 1;     
}  
	if (ok)         
		printf("%d\n", ret);     
	else        
		printf("-1\n"); }  
int main() 
{ 
	int i, j;     
	freopen("barbar.in", "r", stdin);     
	freopen("barbar.out", "w", stdout); 
   
	scanf("%d %d", &n, &m); 
	memset(d, INF, sizeof(d)); 
	for (i = 0; i < n; ++i)     
	{ 
		scanf("%s", s[i]); 
	for (j = 0; j < m; ++j)         
	{             
		if (s[i][j] == 'D')             
		{                
			q[++k] = mp(i, j);                 
			d[i][j] = 0;} 
	if (s[i][j] == 'O')                	
		O = mp(i, j);         
	}     
} 
getDistance(); 
binSearch(); 
}