#include <cstdio>
#include <queue>
#include <cstring>

using namespace std;

const int NMAX = 1005;
int a[NMAX][NMAX];
int dp[NMAX][NMAX];
bool viz[NMAX][NMAX];
int dx[] = {1,0,-1,0};
int dy[] = {0,1,0,-1};
int m , n;
int x1,x2,y1,y2;

struct cell{
int x,y;
};
queue<cell>q;
queue<cell>q1;
inline void qClear(){while(!q.empty()) q.pop();}
inline void init(){memset(viz,0,sizeof(viz));qClear();}
inline bool inMatrix(int x,int y){return(x<=m&&x>=1&&y>=1&&y<=n);}

inline bool verif(int med)
{
    init();
    cell temp,temp1;
    temp.x = x1;
    temp.y = y1;
    q.push(temp);
    while(!q.empty())
    {
        temp = q.front();
        q.pop();
        for(int i = 0 ; i < 4 ; i++)
        {
            temp1.x = temp.x + dx[i];
            temp1.y = temp.y + dy[i];
            if(!inMatrix(temp1.x,temp1.y)) continue;
            if(a[temp1.x][temp1.y] == -2 || a[temp1.x][temp1.y] == -1 || viz[temp1.x][temp1.y] || dp[temp1.x][temp1.y] < med) continue;
            if(temp1.x == x2 && temp1.y == y2)
                return true;
            viz[temp1.x][temp1.y] = 1;
            q.push(temp1);
        }
    }
    return (viz[x2][y2]);
}

int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    char ch;
    scanf("%d%d\n",&m,&n);
    for(int i = 1 ; i <= m ; i++)
    {
        for(int j = 1 ; j < n ; j++)
        {
            scanf("%c",&ch);
            if(ch == 'I')
            {
                x1 = i;
                y1 = j;
                continue;
            }
            if(ch == 'O')
            {
                x2 = i;
                y2 = j;
                continue;
            }
            if(ch == '*')
            {
                a[i][j] = -1;
                continue;
            }
            if(ch == 'D')
            {
                a[i][j] = -2;
                cell temp;
                temp.x = i;
                temp.y = j;
                q1.push(temp);
                continue;
            }
        }
        scanf("%c\n",&ch);
    }
    cell temp;
    while(!q1.empty())
    {
        temp = q1.front();
        q1.pop();
        for(int i = 0 ; i < 4 ; i++)
        {
            cell temp1;
            temp1.x = temp.x + dx[i];
            temp1.y = temp.y + dy[i];
            if(!inMatrix(temp1.x,temp1.y)) continue;
            if(a[temp1.x][temp1.y] == -2 || a[temp1.x][temp1.y] == -1 || dp[temp1.x][temp1.y] != 0) continue;
            dp[temp1.x][temp1.y] = dp[temp.x][temp.y] + 1;
            q1.push(temp1);
        }
    }
    int st,dr,med,ans = -1;
    st = 1;
    dr = 1e6;
    while(st <= dr)
    {
        med = (st+dr)/2;
        if(verif(med))
        {
            ans = med;
            st = med+1;
        }
        else
            dr = med-1;
    }
    printf("%d",ans);
    return 0;
}