#include <iostream>
#include <fstream>
#include <queue>
using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");

queue < pair < int, int > > Q;

int dx[4]= {-1,0,1,0};
int dy[4]= {0,1,0,-1};

struct coordonate
{
    int x, y;
} dragon[1000010];

int n, m, k, v[1010][1010], S[1010][1010];
int x1, y1, x2, y2;

void reset()
{
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++)
            S[i][j]=v[i][j];
}

void update(int P)
{
    for(int t=1; t<=k; t++)
        for(int i=0; i<P; i++)
        {
            int xx=dragon[t].x;
            int yy=dragon[t].y;

            //Pe directia Nord

            if(xx-i>=1)
                S[xx-i][yy]=-1;

            //Pe directia Sud

            if(xx+i<=n)
                S[xx+i][yy]=-1;

            //Pe directia Vest

            if(yy-i>=1)
                S[xx][yy-i]=-1;

            //Pe directia Est

            if(yy+i<=m)
                S[xx][yy+i]=-1;
        }
}

bool inauntru(int x, int y)
{
    if(x<1||y<1||x>n||y>m)
        return false;

    return true;
}

bool passed(int x, int y, int P)
{
    reset();
    update(P);

    S[x][y]=1;
    Q.push(make_pair(x,y));

    while(!Q.empty())
    {
        int ii=Q.front().first, jj=Q.front().second;
        Q.pop();

        for(int dir=0; dir<4; dir++)
            if(inauntru(ii+dx[dir],jj+dy[dir])&&!S[ii+dx[dir]][jj+dy[dir]])
            {
                S[ii+dx[dir]][jj+dy[dir]]=S[ii][jj]+1;
                Q.push(make_pair(ii+dx[dir],jj+dy[dir]));
            }
    }

    if(S[x2][y2]>0)
        return true;

    return false;
}

int binary()
{
    int li=1, lf=m, MAX=0;

    while(li<=lf)
    {
        int mid=(li+lf)/2;

        if(passed(x1,y1,mid))
            MAX=mid, li=mid+1;
        else
            lf=mid-1;
    }

    return MAX;
}

int main()
{
    fin >> n >> m;

    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++)
        {
            char c;
            fin >> c;

            if(c=='D')
                v[i][j]=-2, dragon[++k].x=i, dragon[k].y=j;

            else if(c=='*')
                v[i][j]=-1;

            else if(c=='I')
                x1=i, y1=j;

            else if(c=='O')
                x2=i, y2=j;
        }

    int value=binary();

    if(!value)
        fout << "-1";
    else
        fout << value;

    return 0;
}