#include <fstream>
#include <queue>
#define PII pair<int,int>
#define x first
#define y second
#define MP make_pair
using namespace std;
ifstream fin("barbar.in");
ofstream fout("barbar.out");
const int INF = int(1e9) ,  NMAX = 1005 ,
dx[] = {0,1,-1,0} , dy[] = {-1,0,0,1};
int  dmax[NMAX][NMAX] , DD[NMAX][NMAX] , N , M;
char A[NMAX][NMAX];
PII start , stop , now , curr;
queue< PII > Q;
bool check(const PII &p)
{
return (p.x >= 0 && p.y >=0 && p.x < N  && p.y < M && A[p.x][p.y] != '*');
}
 
void read_data()
{
fin>>N>>M , fin.get();
for(int i = 0;i < N;++i)
fin.getline(A[i],NMAX);
for(int i = 0;i < N;++i)
for(int j = 0;j < M;++j) {
DD[i][j] = INF;
dmax[i][j] = -1;
if(A[i][j] == 'I') start = MP(i,j);
else
if(A[i][j] == 'O') stop = MP(i,j);
else
if(A[i][j] == 'D') Q.push(MP(i,j)) , DD[i][j] = 0;
}
}
 
void bf_dragoni()
{
while(!Q.empty())
{
now = Q.front() , Q.pop();
for(int k = 0;k < 4;++k)
{
curr = MP(now.x + dx[k],now.y + dy[k]);
if(check(curr) == false) continue;
if(DD[curr.x][curr.y] > DD[now.x][now.y] + 1)
DD[curr.x][curr.y] = DD[now.x][now.y] + 1 , Q.push(curr);
}
}
}
void bf()
{
A[stop.x][stop.y] = '.';
dmax[start.x][start.y] = DD[start.x][start.y];
for(Q.push(start);!Q.empty();)
{
now = Q.front() , Q.pop();
for(int k = 0;k < 4;++k)
curr = MP(now.x + dx[k],now.y + dy[k]);
if(check(curr) == false) continue;
if(min(DD[curr.x][curr.y],dmax[now.x][now.y]) > dmax[curr.x][curr.y]) {
Q.push(curr);
}
}
}
}
void write(int X[NMAX][NMAX])
{
for(int i = 0;i < N;++i)
{
for(int j = 0;j < M;++j)
fout<<X[i][j]<<" ";
fout<<'\n';
}
}
int main()
{
read_data();
bf_dragoni();
bf();
fout<<dmax[stop.x][stop.y];
return 0;
}