#include <bits/stdc++.h>
#define fi first
#define se second

using namespace std;

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

const int CNST=1e4;
char ch[1005][1005];
int viz[1005][1005],Lee[1005][1005],dx[4],dy[4],n,m;
queue <pair <int,int>> q;
priority_queue <pair <int,pair <int,int>>> h;

void MakeDs(){
    dx[1]=0;
    dx[3]=0;
    dx[0]=-1;
    dx[2]=1;
    dy[0]=0;
    dy[2]=0;
    dy[1]=1;
    dy[3]=-1;
    return;
}

bool IsInMatrix(int i,int j){
    if (i<1 or n<i)
        return 0;
    if (j<1 or m<j)
        return 0;
    return 1;
}

bool IsWalkable(int i,int j){
    if (ch[i][j]=='I' or ch[i][j]=='O' or ch[i][j]=='.') return 1;
    return 0;
}

void Lee_Function() {
    while (!q.empty()) {
        int x=q.front().first,y=q.front().second;
        q.pop();
        for (int k=0;k<=3;k++) {
            int nx=x+dx[k],ny=y+dy[k];
            if (IsInMatrix(nx,ny)==1 and Lee[nx][ny]==CNST) {
                Lee[nx][ny]=Lee[x][y]+1;
                q.push({nx,ny});
            }
        }
    }
    return;
}

signed main()
{
    ios::sync_with_stdio(false);
    in.tie(NULL);
    out.tie(NULL);
    MakeDs();
    in>>n>>m;
    int ist=0,jst=0;
    int ifn=0,jfn=0;
    for (int i=1;i<=n;++i) {
        for (int j=1;j<=m;++j) {
            in>>ch[i][j];
            Lee[i][j]=CNST;
            if (!IsWalkable(i,j))
                Lee[i][j]+=CNST;
            if (ch[i][j]=='I') {
                ist=i;
                jst=j;
            }
            if (ch[i][j]=='O') {
                ifn=i;
                jfn=j;
            }
        }
    }
    for (int i=1;i<=n;++i)
        for (int j=1;j<=m;++j)
            if (ch[i][j]=='D') {
                q.push({i,j});
                Lee[i][j]=0;
            }
    Lee_Function();
    h.push({Lee[ist][jst],{ist,jst}});
    viz[ist][jst]=1;
    int ans=Lee[ist][jst];
    bool loob=0;
    while (!h.empty()) {
        int x=h.top().se.fi,y=h.top().se.se;
        ans=ans>Lee[x][y] ? Lee[x][y]:ans;
        if (x==ifn and y==jfn) {
            loob=1;
            break;
        }
        h.pop();
        for (int k=0;k<=3;++k) {
            int nx = x+dx[k], ny = y+dy[k];
            if (IsInMatrix(nx,ny) and IsWalkable(nx,ny)==1 and viz[nx][ny]==0) {
                h.push({Lee[nx][ny],{nx,ny}});
                viz[nx][ny]=1;
            }
        }
    }
    if (loob==0)
        ans=-1;
    out<<ans;
    return 0;
}