#include<stdio.h>      
#define INF 1000
     
struct dragon {int x,y;}d[1000005];      
     
int a1,b1,viz[1005][1005],xi,yi,xf,yf,mij,sol,min,max,m1,p,u,c[2][1000005],M[1005][1005],a,b,dr,i,n,j,di[1000005],D[2][5]={{0,1,0,-1},{1,0,-1,0}};      
     
char m[1005][1005];      
     
     
int drum(int k){      
     
  p=u=1;      
  c[0][p]=xf;      
  c[1][p]=yf;      
  viz[xf][yf]=k;      
     
    while(p<=u){      
     
     
       for(j=0;j<=3;j++){      
       a=c[0][p]+D[0][j];      
       b=c[1][p]+D[1][j];      
     
     if(viz[a][b]!=k&&M[a][b]>=k&&m[a][b]!='*'&&a>=1&&a<=n&&b>=1&&b<=m1){      
     u++;      
     c[0][u]=a;      
     c[1][u]=b;      
     viz[a][b]=k;      
     
         if(a==xi&&b==yi)      
         return 1;      
     
     }      
     
       }      
     
     
    p++;      
    }      
     
     
     
return 0;      
}      
     
     
     
int main(){      
     
FILE *f=fopen("barbar.in","r");      
fscanf(f,"%d %d\n",&n,&m1);      
     
for(i=1;i<=n;i++)      
m[i][0]='0';      
     
     
  for(i=1;i<=n;i++){      
     
    for(j=1;j<=m1;j++){      
    fscanf(f,"%c",&m[i][j]);      
     
      if(m[i][j]=='D'){      
      dr++;      
      d[dr].x=i;      
      d[dr].y=j;      
      }      
     
     
      if(m[i][j]=='O'){      
      xf=i;      
      yf=j;      
      }      
     
     
      if(m[i][j]=='I'){      
      xi=i;      
      yi=j;      
      }      
     
     
    }      
     
     
  fscanf(f,"\n");      
  }      
     
fclose(f);      
     
     
for(i=1;i<=n;i++){   
  for(j=1;j<=m1;j++){   
  M[i][j]=INF;   
  viz[i][j]=-1;   
  }   
}   
     
     
max=-INF;      
min=INF;      
     
  for(i=1;i<=dr;i++){      
  p=u=1;      
  c[0][p]=d[i].x;      
  c[1][p]=d[i].y;      
  M[c[0][p]][c[1][p]]=0;      
  di[p]=0;      
     
     while(p<=u){      
     
     
       for(j=0;j<=3;j++){      
       a=c[0][p]+D[0][j];      
       b=c[1][p]+D[1][j];      
     
     if(M[a][b]>di[p]+1&&m[a][b]!='*'&&a>=1&&a<=n&&b>=1&&b<=m1){      
     u++;      
     c[0][u]=a;      
     c[1][u]=b;      
     di[u]=di[p]+1;      
     M[a][b]=di[u];      
     
     }      
     
       }      
     
     
     p++;      
     }      
     
     
  }      
     
     
 for(i=1;i<=n;i++)      
     
  for(j=1;j<=m1;j++){      
     
    if(M[i][j]>max&&M[i][j]!=INF)      
    max=M[i][j];      
     
     
  }      
     
     
  a1=0;      
  b1=max;      
     
     
  sol=-1;      
     
    while(a1<=b1){      
     
     mij=(a1+b1)/2;      
     
       if(drum(mij)){      
       sol=mij;      
       a1=mij+1;      
       }      
     
       else     
       b1=mij-1;      
     
     
     
    }      
     
     
FILE *g=fopen("barbar.out","w");      
     
fprintf(g,"%d",sol);      
     
fclose(g);      
     
     
return 0;      
}