#include<stdio.h>
#define INF 20

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;
}