#include <fstream>
#include <queue>
#include <bitset>
#include <cstdio>
#include <cstring>
#define N 1010
#define INF 9999999
#define PI pair<int, int>
#define x first
#define y second
#define mp make_pair

using namespace std;

FILE* fin=fopen("barbar.in","r");
FILE* fout=fopen("barbar.out","w");
const int maxb=8192;
char buf[maxb];
int ptr=0;

inline int getint() {
    int nr=0;
    while(buf[ptr]<'0'||'9'<buf[ptr])
        if (++ptr>=maxb) fread(buf,maxb,1,fin),ptr=0;
    while ('0'<=buf[ptr]&&buf[ptr]<='9') {
        nr=nr*10+buf[ptr]-'0';
        if (++ptr>=maxb) fread(buf,maxb,1,fin),ptr=0;
    }
    return nr;
}

inline char zgetchar()
{
    char c;
    while(buf[ptr]!='I' && buf[ptr]!='O' && buf[ptr]!='D' && buf[ptr]!='.' && buf[ptr]!='*')
        if (++ptr>=maxb) fread(buf,maxb,1,fin),ptr=0;
    c=buf[ptr];
    if (++ptr>=maxb) fread(buf,maxb,1,fin),ptr=0;
    return c;
}


int n,m,i,j,A[N][N],D[N][N],C[N][N],l1,c1,l2,c2,z;
char s;
queue<PI> Q;
bool InQue[N][N];

const int dx[4]={-1,0,1,0};
const int dy[4]={0,1,0,-1};

bool Ok1 (int i, int j, int l, int c)
{
    if (l<1 || l>n || c<1 || c>m) return 0;
    if (D[i][j]+1>=D[l][c]) return 0;
    if (A[l][c]!=0) return 0;
    return 1;
}

bool Ok2 (int i, int j, int l, int c)
{
    if (l<1 || l>n || c<1 || c>m) return 0;
    if (A[l][c]!=0) return 0;
    if (min(D[l][c],C[i][j])<=C[l][c]) return 0;
    return 1;
}

void Lee1 ()
{
    while (!Q.empty())
    {
        i=Q.front().x;
        j=Q.front().y;
        Q.pop();
        InQue[i][j]=0;
        for (int d=0;d<4;d++)
            if (Ok1(i,j,i+dx[d],j+dy[d]))
            {
                D[i+dx[d]][j+dy[d]]=D[i][j]+1;
                if (!InQue[i+dx[d]][j+dy[d]])
                {
                    Q.push(mp(i+dx[d],j+dy[d]));
                    InQue[i+dx[d]][j+dy[d]]=1;
                }
            }
    }
}

bool Lee2 (int STOP)
{
    memset(C,0,sizeof(C));
    memset(InQue,0,sizeof(InQue));
    Q.push(mp(l1,c1));
    C[l1][c1]=D[l1][c1];
    while (!Q.empty())
    {
        i=Q.front().x;
        j=Q.front().y;
        Q.pop();
        InQue[i][j]=0;
        for (int d=0;d<4;d++)
            if (Ok2(i,j,i+dx[d],j+dy[d]))
            {
                if (min(C[i][j],D[i+dx[d]][j+dy[d]])<STOP) continue;
                C[i+dx[d]][j+dy[d]]=min(C[i][j],D[i+dx[d]][j+dy[d]]);
                if (!InQue[i+dx[d]][j+dy[d]])
                {
                    Q.push(mp(i+dx[d],j+dy[d]));
                    InQue[i+dx[d]][j+dy[d]]=1;
                }
                if (i+dx[d]==l2 && j+dy[d]==c2) return 1;
            }
    }
    return 0;
}

int Search ()
{
    int p=1,u=D[l1][c1],ANS=-1,m;

    while (p<=u)
    {
        m=(p+u)/2;
        if (Lee2(m))
        {
            ANS=m;
            p=m+1;
        }
        else u=m-1;
    }
    return ANS;
}


int main ()
{
    n=getint();m=getint();
    for (i=1;i<=n;i++)
        for (j=1;j<=m;j++)
        {
            D[i][j]=INF;
            C[i][j]=-1;
        }
    for (i=1;i<=n;i++)
    {
        for (j=1;j<=m;j++)
        {
            z=0;
            s=zgetchar();
            if (s=='*') z=-1;
            if (s=='I')
            {
                l1=i;
                c1=j;
            }
            if (s=='O')
            {
                l2=i;
                c2=j;
            }
            if (s=='D')
            {
                z=-2;
                Q.push(mp(i,j));
                InQue[i][j]=1;
                D[i][j]=0;
            }
            A[i][j]=z;
        }
    }
    Lee1();
    fprintf(fout,"%d\n",Search());
    fclose(fin);fclose(fout);
    return 0;
}