#include<stdio.h>
#include<string.h>
 
typedef struct punct
{
    int x,y;
}punct;
 
punct q[2000100],aux,I,O;
int v[1005][1005];
 
int n,m,st=1,sf,d[1005][1005],dx[]={-1,0,1,0},dy[]={0,1,0,-1},dist;
int sol[1005][1005];
 
void fill()
{
    int i,x,y;
    while(st<=sf)
    {
        aux=q[st];
        ++st;
        for(i=0;i<4;++i)
        {
            x=aux.x+dx[i];
            y=aux.y+dy[i];
            if((x>=1&&y>=1&&x<=n&&y<=m) &&v[x][y]==-1)
            {
                ++sf;
                q[sf].x=x;
                q[sf].y=y;
                v[x][y]=v[aux.x][aux.y]+1;
            }
        }
    }
}
 
int lee()
{
    int i,x,y,a=0;
    if(v[I.x][I.y]<dist)
        return a;
    sf=st=1;
    q[st]=I;
    memset(d,0,sizeof(d));
    while(st<=sf&&a==0)
    {
        aux=q[st];
        for(i=0;i<4;++i)
        {
            x=aux.x+dx[i];
            y=aux.y+dy[i];
            if((x>=1&&y>=1&&x<=n&&y<=m) &&d[x][y]==0&&v[x][y]>=dist)
            {
                ++sf;
                q[sf].x=x;
                q[sf].y=y;
                d[x][y]=1;
                if(x==O.x&&y==O.y)
                {
                    a=1;
                    break;
                }
            }
        }++st;
    }
    return a;
}
 
int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    int i,j,S,D;
    char c;
    scanf("%d%d\n",&n,&m);
    for(i=1;i<=n;++i)
    {
        for(j=1;j<=m;++j)
        {
            scanf("%c",&c);
            if(c=='.')
                v[i][j]=-1;
            if(c=='*')
                v[i][j]=-2;
            else if(c=='D')
            {
                aux.x=i;aux.y=j;
                q[++sf]=aux;
            }
            else if(c=='I')
            {I.x=i;I.y=j;v[i][j]=-1;}
            else if(c=='O')
            {O.x=i;O.y=j;v[i][j]=-1;}
        }
        scanf("\n");
    }
    //////////////////////////
    fill();
 
    S=0;D=n*m;
    while(S<=D)
    {
        dist=(S+D)/2;
        if(lee())
            S=dist+1;
        else
            D=dist-1;
    }
 
    if(D>=0)
        printf("%d\n",D);
    else
        printf("-1\n");
 
    /*for(i=1;i<=n;++i)
    {
        for(j=1;j<=m;++j)
            printf("%2d ",v[i][j]);
        printf("\n");
    }*/
 
    return 0;
}