#include <cstdio>
#include <queue>
#include <iostream>

using namespace std;

const int NMAX = 1000;

char v[NMAX+3][NMAX+3];

int a[NMAX][NMAX];

int r,c;

const int iplus[4] = {0,0,-1,1};
const int jplus[4] = {1,-1,0,0};

struct square
{
    int x,y;
};

bool operator<(const square &c,const square &b)
{
    return a[c.x][c.y] < a[b.x][b.y];
}


priority_queue <square> h;

queue <square> q;

square start,finish;

void makecost()
{
    for(int i = 1;i <= r;i ++)
    {
        for(int j = 1;j <= c;j ++)
        {
            if(v[i][j] == 'D')
                q.push({i,j});
            if(v[i][j] == 'I')
            {
                start = {i,j};
                v[i][j] = '.';
            }
            if(v[i][j] == 'O')
            {
                finish = {i,j};
                v[i][j] = '.';
            }
        }
    }
    while(q.size() > 0)
    {
        square s = q.front();
        q.pop();
        for(int dir = 0;dir < 4;dir ++)
        {
            int x = s.x + iplus[dir];
            int y = s.y + jplus[dir];
            if(v[x][y] == '.' && a[x][y] == 0)
            {
                a[x][y] = a[s.x][s.y] + 1;
                q.push({x,y});
            }
        }
    }

}

bool check[NMAX][NMAX];

bool l[NMAX][NMAX];

void makeanswer()
{
    int minim = 99999999;
    h.push(start);
    while(!h.empty())
    {
        square s = h.top();
        h.pop();

        if(check[s.x][s.y] == 1)
            continue;
        check[s.x][s.y] = 1;

        if(a[s.x][s.y] < minim)
            minim = a[s.x][s.y];
        //printf("%d %d %d\n",s.x,s.y, a[s.x][s.y]);
        if(s.x == finish.x && s.y == finish.y)
        {
            printf("%d\n",minim);
            return ;

        }
        for(int dir = 0;dir < 4;dir ++)
        {
            int x = s.x + iplus[dir];
            int y = s.y + jplus[dir];
            if( v[x][y] == '.' || v[x][y] == 'D' ){
                h.push({x,y});
            }
        }
    }
    printf("-1\n");
    return;
}

int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    scanf("%d %d\n",&r,&c);
    for(int i = 1;i <= r;i ++)
    {
        fgets(v[i]+1,NMAX+3,stdin);
        //fputs(v[i],stdout);
    }
    makecost();
    makeanswer();
    return 0;
}