#include <fstream>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
int n,m,i,j,p,u,c[2][1001*1001],ist,jst,fini,finj,a[1001][1001],b[1001][1001],f[1001][1001],st,dr,mid;
char ch;
int di[]={0,0,-1,1};
int dj[]={-1,1,0,0};
int main (){
fin>>n>>m;
for(i=1;i<=n;i++)
for(j=1;j<=m;j++){
fin>>ch;
if(ch=='.')
a[i][j]=b[i][j]=0;
if(ch=='*'){
a[i][j]=0;
b[i][j]=-1;
}
if(ch=='D'){
a[i][j]=1;
u++;
c[0][u]=i;
c[1][u]=j;
}
if(ch=='I'){
a[i][j]=0;
ist=i;
jst=j;
}
if(ch=='O'){
a[i][j]=0;
fini=i;
finj=j;
}
}
p=1;
while(p<=u){
int ic=c[0][p];
int jc=c[1][p];
for(int d=0;d<4;d++){
int iv=ic+di[d];
int jv=jc+dj[d];
if(iv>=1&&iv<=n&&jv>=1&&jv<=m&&a[iv][jv]==0){
a[iv][jv]=1+a[ic][jc];
u++;
c[0][u]=iv;
c[1][u]=jv;
}
}
p++;
}
for(i=1;i<=n;i++)
for(j=1;j<=m;j++)
if(b[i][j]!=-1)
b[i][j]=a[i][j];
st=1;
dr=1001*1001;
while(st<=dr){
mid=(st+dr)/2;
p=u=1;
for(i=1;i<=n;i++)
for(j=1;j<=m;j++)
f[i][j]=0;
c[0][p]=ist;
c[1][p]=jst;
f[ist][jst]=1;
while(p<=u){
int ic=c[0][p];
int jc=c[1][p];
for(int d=0;d<4;d++){
int iv=ic+di[d];
int jv=jc+dj[d];
if(iv>=1&&iv<=n&&jv>=1&&jv<=m&&b[iv][jv]>=mid&&f[iv][jv]==0){
f[iv][jv]=1;
u++;
c[0][u]=iv;
c[1][u]=jv;
}
}
p++;
}
if(f[fini][finj]==0)
dr=mid-1;
else
st=mid+1;
}
fout<<dr-1;
return 0;
}