#include<cstdio>
#include<queue>
#include<cstring>
#define MAXN 1010
using namespace std;
queue<pair<int,int> > Queue;
pair<int,int> start,finish;
int a[MAXN][MAXN],dragon[MAXN][MAXN],seen[MAXN][MAXN],n,m;
int line[4]={0,1,0,-1};
int column[4]={1,0,-1,0};
bool Valid(int l,int c){
    if(l<1||l>n||c<1||c>m)
        return false;
    return true;
}
void Precompute(){
    int l,c,k,newL,newC;
    while(!Queue.empty()){
        l=Queue.front().first;
        c=Queue.front().second;
        Queue.pop();
        for(k=0;k<4;k++){
            newL=l+line[k];
            newC=c+column[k];
            if(dragon[newL][newC]==-1&&Valid(newL,newC)==true){
                dragon[newL][newC]=dragon[l][c]+1;
                Queue.push(make_pair(newL,newC));
            }
        }
    }
}
bool Check(int value){
    int l,c,k,newL,newC;
    memset(seen,0,sizeof(seen));
    if(dragon[start.first][start.second]<value)
        return false;
    Queue.push(start);
    seen[start.first][start.second]=1;
    while(!Queue.empty()){
        l=Queue.front().first;
        c=Queue.front().second;
        Queue.pop();
        for(k=0;k<4;k++){
            newL=l+line[k];
            newC=c+column[k];
            if(a[newL][newC]==0&&Valid(newL,newC)==true&&dragon[newL][newC]>=value&&seen[newL][newC]==0){
                seen[newL][newC]=1;;
                Queue.push(make_pair(newL,newC));
            }
        }
    }
    if(seen[finish.first][finish.second]==0)
        return false;
    return true;
}
int BinarySearch(){
    int answer=-1,middle,left=1,right=m+n;
    while(left<=right){
        middle=(left+right)/2;
        if(Check(middle)==true){
            answer=middle;
            left=middle+1;
        }
        else
            right=middle-1;
    }
    return answer;
}
int main(){
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    int i,j;
    char ch;
    scanf("%d%d\n",&n,&m);
    for(i=1;i<=n;i++){
        for(j=1;j<=m;j++){
            scanf("%c",&ch);
            dragon[i][j]=-1;
            if(ch=='.')
                a[i][j]=0;
            if(ch=='D'){
                Queue.push(make_pair(i,j));
                dragon[i][j]=0;
            }
            if(ch=='I')
                start=make_pair(i,j);
            if(ch=='O')
                finish=make_pair(i,j);
            if(ch=='*')
                a[i][j]=-1;
        }
        scanf("%c",&ch);
    }
    Precompute();
    printf("%d",BinarySearch());
    return 0;
}