#include<stdio.h>
#include<string.h>

typedef struct punct
{
    int x,y;
}punct;

punct q[2000100],aux,I,O;
char v[1005][1005];

int n,m,st=1,sf,d[1005][1005],sol[1005][1005],dx[]={1,-1,0,0},dy[]={0,0,1,-1},dist;

inline int min(int a,int b)
{return a<b?a:b;}

void fill()
{
    int k,i,x,y;
    while(st<=sf)
    {
        aux=q[st];
        ++st;
        k=d[aux.x][aux.y];
        for(i=0;i<4;++i)
        {
            x=aux.x+dx[i];
            y=aux.y+dy[i];
            if((x>=0&&y>=0&&x<n&&y<m) &&v[x][y]=='.'&&(d[x][y]==0||d[x][y]>k+1))
            {
                ++sf;
                q[sf].x=x;
                q[sf].y=y;
                d[x][y]=k+1;
            }
        }
    }
}

int lee()
{
    int k,i,x,y,a=0;
    if(d[aux.x][aux.y]<dist)
        return a;
    memset(sol,0,sizeof(sol));
    while(st<=sf&&a==0)
    {
        aux=q[st];
        ++st;
        k=sol[aux.x][aux.y];
        for(i=0;i<4;++i)
        {
            x=aux.x+dx[i];
            y=aux.y+dy[i];
            if((x>=0&&y>=0&&x<n&&y<m) &&v[x][y]=='.'&&(sol[x][y]==0||sol[x][y]>=dist))
            {
                ++sf;
                q[sf].x=x;
                q[sf].y=aux.y+dy[i];
                sol[x][y]=min(k,d[x][y]);
                if(x==O.x&&y==O.y)
                {
                    a=1;
                    break;
                }
            }
        }
    }
    return a;
}

int main()
{
    freopen("barbar.in","r",stdin);
    freopen("barbar.out","w",stdout);
    int i,j,S,D;
    scanf("%d%d\n",&n,&m);
    for(i=0;i<n;++i)
        scanf("%s\n",v[i]);

    for(i=0;i<n;++i)
    {
        for(j=0;j<m;++j)
        {
            if(v[i][j]=='.')
                continue;
            if(v[i][j]=='D')
            {
                aux.x=i;aux.y=j;
                q[++sf]=aux;
            }
            else if(v[i][j]=='I')
            {I.x=i;I.y=j;v[i][j]='.';}
            else if(v[i][j]=='O')
            {O.x=i;O.y=j;v[i][j]='.';}

        }
    }
    //////////////////////////
    fill();

    sf=st=1;
    q[sf]=I;
    sol[q[sf].x][q[sf].y]=d[q[sf].x][q[sf].y];

    S=0;D=n*m;
    while(S<=D)
    {
        dist=(S+D)/2;
        if(lee())
            S=dist+1;
        else
            D=dist-1;
    }

    if(D)
        printf("%d\n",D);
    else
        printf("-1\n");
    return 0;
}