#include<stdio.h>

long int a[1100][1100], n, m, x1, y1, x2, y2, nr, b[1100][1100];
long int dx[4]={0,1,0,-1}, dy[4]={1,0,-1,0};

typedef struct
{
  long int x, y;
} Coada;

Coada c[2000000];


void citire()
{
  freopen("barbar.in","r",stdin);
  freopen("barbar.out","w",stdout);
  scanf("%ld %ld",&n,&m);
  long int i, j;
  char x;
  scanf("\n");
  for (i=1; i<=n; i++)
  {
    for (j=1; j<=m; j++)
    {
      scanf("%c",&x);
      switch(x)
      {
	case '.' : {a[i][j]=-1; break;}
	case '*' : {a[i][j]=-2; break;}
	case 'D' : {a[i][j]=0; c[++nr].x=i; c[nr].y=j;break;}
	case 'I' : {x1=i, y1=j, a[i][j]=-1; break;}
	case 'O' : {x2=i, y2=i, a[i][j]=-1; break;}
      }
    }
    scanf("\n");
  }
  for (i=1; i<=n; i++) a[i][0]=a[i][m+1]=-2;
  for (i=1; i<=m; i++) a[0][i]=a[n+1][i]=-2;
}


void parcurg()
{
  long int p, u, x, y, i;
  p=1;
  u=nr;
  while (p<=u)
  {
    for (i=0; i<4; i++)
    {
     x=c[p].x+dx[i];
     y=c[p].y+dy[i];
     if (a[x][y]!=-2)
     {
       if (a[x][y]==-1)
       {
	 u++;
	 c[u].x=x;
	 c[u].y=y;
	 a[x][y]=a[c[p].x][c[p].y]+1;
       }
     }
    }
    p++;
  }
}


int verif (int dist)
{
  long int p, u, x, y, i;
  p=1;
  u=1;
  c[1].x=x1; c[1].y=y1;
  while (p<=u)
  {
    for (i=0; i<4; i++)
    {
      x=c[p].x+dx[i];
      y=c[p].y+dy[i];
      if (a[x][y]>=dist && b[x][y]!=dist-1)
        {
	  u++;
	  c[u].x=x;
	  c[u].y=y;
	  b[x][y]=dist-1;
	  if (x==x2 && y==y2) return 1;
        }    
    }
    p++;
  }
  return 0;
}

/*
int caut()
{
  int p, u, m;
  p=0; u=1010; 
  m=(p+u)/2;
  while (p<u)
  {
    if (verif(m) && !verif(m+1)) return m;
    else if (verif(m) && verif(m+1)) {p=m; m=(p+u)/2;}
         else  {u=m; m=(p+u)/2;}
  }
  return -1;
}
*/

int main()
{
  citire();
  parcurg();
  long int i=n*m;
    while (!verif(i) && i>=0)  i--;
    printf("%ld",i);

  return 0;
}