#include<cstdio>
 
const int N=1<<10;
 
const int dx[]={-1,0,1,0};
const int dy[]={0,1,0,-1};
 
char s[N][N];
int x1[N*N],y1[N*N],x[N*N],y[N*N],nn,a[N][N],n,m,nr,xs,ys,xxi,yyi;
bool fr[N][N];
 
bool dragon(int xx,int yy)
{
    if (s[xx][yy]=='D')
        return true;
    return false;
}
 
bool liber(int xx,int yy)
{
    if (s[xx][yy]=='.' || s[xx][yy]=='I' || s[xx][yy]=='O')
        return true;
    return false;
}
 
void lee(int xx,int yy)
{
    if (xx-1>=0 && liber(xx-1,yy) && (a[xx-1][yy]>a[xx][yy]+1 || a[xx-1][yy]==0))
    {
        nn++;
        x1[nn]=xx-1;
        y1[nn]=yy;
        a[xx-1][yy]=a[xx][yy]+1;
    }
    if (yy+1<m && liber(xx,yy+1) && (a[xx][yy+1]>a[xx][yy]+1 || a[xx][yy+1]==0))
    {
        nn++;
        x1[nn]=xx;
        y1[nn]=yy+1;
        a[xx][yy+1]=a[xx][yy]+1;
    }
    if (xx+1<n && liber(xx+1,yy) && (a[xx+1][yy]>a[xx][yy]+1 || a[xx+1][yy]==0))
    {
        nn++;
        x1[nn]=xx+1;
        y1[nn]=yy;
        a[xx+1][yy]=a[xx][yy]+1;
    }
    if (yy-1>=0 && liber(xx,yy-1) && (a[xx][yy-1]>a[xx][yy]+1 || a[xx][yy-1]==0))
    {
        nn++;
        x1[nn]=xx;
        y1[nn]=yy-1;
        a[xx][yy-1]=a[xx][yy]+1;
    }
}
 
void init()
{
    nr=0;
    for (int i=0;i<n;i++)
        for (int j=0;j<m;j++)
            if (s[i][j]=='O')
            {
                xs=i;
                ys=j;
            }
            else
            if (s[i][j]=='I')
            {
                xxi=i;
                yyi=j;
            }
}
 
bool ok(int d)
{
    for (int i=0;i<n;i++)
        for (int j=0;j<m;j++)
            fr[i][j]=false;
    int p,u,pcx,pcy,pux,puy;
    p=u=0;
    x[u]=xxi;
    y[u++]=yyi;
    if (a[xxi][yyi]<d)
        return false;
    fr[xxi][yyi]=true;
    while (p<u)
    {
        pcx=x[p];
        pcy=y[p++];
        for(int i=0 ; i<4 ; ++i)
        {
            pux=pcx+dx[i];
            puy=pcy+dy[i];
            if (pux>=0 && pux<n && puy>=0 && puy<m && a[pux][puy]>=d && !fr[pux][puy])
            {
                x[u]=pux;
                y[u++]=puy;
                fr[pux][puy]=true;
            }
        }
    } 
    return fr[xs][ys];
}
 
int cautbin()
{
    int pas=1<<12,i;
    for (i=0;pas;pas>>=1)
        if (ok(i+pas))
            i+=pas;
    return i;
}
 
int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    scanf("%d%d\n",&n,&m);
    nr=0;
    for (int i=0;i<n;i++)
    {
        gets(s[i]);
        for (int j=0;s[i][j];j++)
            if (dragon(i,j))
            {
                nr++;
                x[nr]=i;
                y[nr]=j;
            }
    }
    while (nr)
    {
        nn=0;
        for (int i=1;i<=nr;i++)
            lee(x[i],y[i]);
        nr=nn;
        for (int i=1;i<=nr;i++)
        {
            x[i]=x1[i];
            y[i]=y1[i];
        }
    }
    init();
    int x=cautbin();
    if (x==0)
        x=-1;
    printf("%d\n",x);
    return 0;
}