#include <bits/stdc++.h>
using namespace std;
ifstream f("barbar.in");
ofstream g("barbar.out");
int n,m,i,j,nr,q,w,step,x,y,X,Y,D[1<<10][1<<10],viz[1<<10][1<<10];
int dx[]={-1,1,0,0};
int dy[]={0,0,-1,1};
bool OK[1<<10][1<<10];
char M[1<<10][1<<10];
queue <pair <int,int> > Q;
bool check(int dist)
{
    ++nr;
    if(D[x][y]>=dist) Q.push(make_pair(x,y));
    while(!Q.empty())
    {
        q=Q.front().first;
        w=Q.front().second;
        Q.pop();
        if(viz[q][w]==nr) continue;
        viz[q][w]=nr;
        for(i=0;i<4;++i)
        {
            int l=q+dx[i];
            int c=w+dy[i];
            if(!OK[l][c]&&D[l][c]>=dist)
                Q.push(make_pair(l,c));
        }
    }
    return (viz[X][Y]==nr);
}
int main()
{
    f>>n>>m;
    for(i=1;i<=n;++i)
        for(j=1;j<=m;++j) D[i][j]=1<<30;
    for(i=1;i<=n;++i)
    {
        f>>(M[i]+1);
        for(j=1;j<=m;++j)
        {
            if(M[i][j]=='I') x=i,y=j;
            if(M[i][j]=='O') X=i,Y=j;
            if(M[i][j]=='D')
            {
                Q.push(make_pair(i,j));
                D[i][j]=0;
            }
        }
    }
    for(i=0;i<=n+1;++i)
        for(j=0;j<=m+1;++j)
            if(!i||!j||i==n+1||j==m+1||M[i][j]=='*') OK[i][j]=1;
    ++nr;
    while(!Q.empty())
    {
        q=Q.front().first;
        w=Q.front().second;
        Q.pop();
        if(viz[q][w]==nr) continue;
        viz[q][w]=nr;
        for(i=0;i<4;++i)
        {
            int l=q+dx[i];
            int c=w+dy[i];
            if(!OK[l][c]&&D[l][c]>D[q][w]+1)
            {
                D[l][c]=D[q][w]+1;
                Q.push(make_pair(l,c));
            }
        }
    }
    ++nr;
    Q.push(make_pair(x,y));
    while(!Q.empty())
    {
        q=Q.front().first;
        w=Q.front().second;
        Q.pop();
        if(viz[q][w]==nr) continue;
        viz[q][w]=nr;
        for(i=0;i<4;++i)
           if(!OK[q+dx[i]][w+dy[i]]&&M[q+dx[i]][w+dy[i]]!='D')
                Q.push(make_pair(q+dx[i],w+dy[i]));
    }
    if(viz[X][Y]!=nr)
    {
        g<<-1;
        return 0;
    }
    int sol=0;
    for(step=1<<8;step;step>>=1)
        if(sol+step<=min(n,m))
            if(check(sol+step)) sol+=step;
    g<<sol;
    return 0;
}