#include <fstream>
#include <queue>
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");


struct poz{
int x;
int y;}start_,exit_;
queue <poz> q;
int n,m;
int dp[1005][1005];
int v[1005][1005];
bool marc[1005][1005];

int dx[]={1,-1,0,0};
int dy[]={0,0,-1,1};



inline bool inmat(int i,int j)
{
    return i>=1 && i<=n && j>=1 && j<=m;
}

bool sol(int val)
{
    if(dp[start_.x][start_.y]<=val)
        return false;
    if(dp[exit_.x][exit_.y]<=val)
        return false;
    q.push(start_);
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            marc[i][j]=false;
        }
    }
    while(!q.empty())
    {
        poz fr = q.front();
        q.pop();
        for(int d=0;d<=3;d++)
        {
            int l = fr.x+dx[d];
            int c = fr.y+dy[d];
            if(inmat(l,c) && !v[l][c] && dp[l][c]>val && marc[l][c]==false)
            {
                q.push({l,c});
                marc[l][c]=true;
            }
        }
    }
    return marc[exit_.x][exit_.y];

}

void bins()
{
    int st=1;
    int dr=n*m+1;
    int rez=-1;
    while(st<=dr)
    {
        int mid = (st+dr)/2;
        if(sol(mid))
        {
            rez=mid;
            st=mid+1;
        }
        else
            dr=mid-1;
    }
    fout<<rez;
    return;

}

int main()
{
    fin>>n>>m;
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            char x;
            fin>>x;
            if(x=='D'){

                q.push({i,j});
                dp[i][j]=1;
            }
            else if (x=='*')
            {
                v[i][j]=1;
            }
            else if (x=='I')
            {
                start_.x=i;
                start_.y=j;
            }
            else if (x=='O')
            {
                exit_.x=i;
                exit_.y=j;
            }
        }
    }
    while(!q.empty())
    {
        poz fr = q.front();
        q.pop();
        for(int d=0;d<=3;d++)
        {
            int l = dx[d]+fr.x;
            int c = dy[d]+fr.y;
            if(inmat(l,c) && !v[l][c] && !dp[l][c])
            {
                dp[l][c]=dp[fr.x][fr.y]+1;
                q.push({l,c});
            }
        }
    }
    bins();
}