#include<fstream>
#include<queue>
#include<cstring>
using namespace std;
ifstream f("barbar.in"); ofstream g("barbar.out");
int a[1005][1005], d[1005][1005], viz[1005][1005];
int dl[]={0,1,0,-1};
int dc[]={-1,0,1,0};
struct nod {int x,y;} start, stop, temp, nou;
queue <nod> q;
bool traseu(int p)
{   if(d[start.x][start.y]<p) return 0;
    q.push(start);
    memset(viz,0,sizeof(viz));
    viz[start.x][start.y]=1;
    while(!q.empty())
    {   temp=q.front(); q.pop();
        for(int lin,col,k=0; k<4; ++k)
        {   lin =temp.x+dl[k]; col =temp.y+dc[k];
            if(d[lin][col]>=p && !viz[lin][col])
            {   viz[lin][col]=1;
                nou.x=lin; nou.y=col; q.push(nou);
            }
        }
    }
    return viz[stop.x][stop.y];
}
int main()
{   int n, m;    char ch;
    f>>n>>m;
    for(int i=1; i<=n; ++i)
        for(int j=1; j<=m; ++j)
            d[i][j]=-2;
		for(int i=0; i<=n+1; ++i) d[i][0]=d[i][m+1]=-1;
    for(int i=0; i<=m+1; ++i) d[0][i]=d[n+1][i]=-1;
    for(int i=1; i<=n; ++i)
        for(int j=1; j<=m; ++j)
        {   f>>ch;
            switch(ch)
            {   case '*' : d[i ][j]=-1; break;
                case 'O' : stop.x=i; stop.y=j; break;
                case 'I' : start.x=i; start.y=j; break;
                case 'D' : d[i][j]=0; nou.x=i; nou.y=j; q.push(nou); break;
            }
        }
    while(!q.empty())
    {   temp=q.front(); q.pop();
        for(int lin,col,k=0; k<4; ++k)
            {lin =temp.x+dl[k]; col =temp.y+dc[k];
             if(d[lin][col]==-2)
                {d[lin][col]=d[temp.x][temp.y]+1; nou.x=lin; nou.y=col; q.push(nou);}
            }
    }
    int dist=-1;
    if(d[start.x][start.y] !=-2)
    {   int st=0, dr=n*m, mij;
        while(st<=dr)
        {   mij=(st+dr)>>1;
            if(traseu(mij)) {dist=mij; st=mij+1;} else dr=mij-1;
        }
    }
    g<<dist<<'\n'; return 0;
}