#include<stdio.h>   
#define INF 200
  
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;   
  
  
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;   
}