#include <fstream>
#include <vector>
#include <queue>
using namespace std;
ifstream cin("barbar.in");
ofstream cout("barbar.out");
char a[1005][1005];
int dist[1005][1005];
int m[1005][1005];
void dragonlee(int r, int c, vector <pair <int, int>> v){
const int dirx[] = {0, 0, 1, -1};
const int diry[] = {1, -1, 0, 0};
queue <pair <int, int>> Q;
for(auto elem : v){
Q.push(elem);
dist[elem.first][elem.second] = 0;
}
auto inside = [&r, &c](const pair <int, int>& cell) -> bool {
return 1 <= cell.first && cell.first <= r && 1 <= cell.second && cell.second <= c;
};
while(!Q.empty()){
auto cell = Q.front();
Q.pop();
for(int dir = 0; dir <= 3; dir ++){
pair <int, int> x = make_pair(cell.first + dirx[dir], cell.second + diry[dir]);
if(!inside(x) || a[x.first][x.second] == '*'){
continue;
}
else if(dist[x.first][x.second] == 0){
dist[x.first][x.second] = dist[cell.first][cell.second] + 1;
Q.push(x);
}
}
}
// cout << inside(make_pair(r, c)) << "\n";
/*cout << inside([0, 1]) << "\n";
cout << inside([1, 0]) << "\n";
cout << inside([0, 0]) << "\n";*/
}
void lee(pair <int, int> start, int k, int r, int c){
const int dirx[] = {0, 0, 1, -1};
const int diry[] = {1, -1, 0, 0};
queue <pair <int, int>> Q;
Q.push(start);
auto inside = [&r, &c](const pair <int, int>& cell) -> bool {
return 1 <= cell.first && cell.first <= r && 1 <= cell.second && cell.second <= c;
};
m[start.first][start.second] = 1;
while(!Q.empty()){
auto cell = Q.front();
Q.pop();
for(int dir = 0; dir <= 3; dir ++){
pair <int, int> x = make_pair(cell.first + dirx[dir], cell.second + diry[dir]);
if(!inside(x) || a[x.first][x.second] == '*' || dist[x.first][x.second] < k){
continue;
}
else if(m[x.first][x.second] == 0){
m[x.first][x.second] = m[cell.first][cell.second] + 1;
Q.push(x);
}
}
}
// cout << inside(make_pair(r, c)) << "\n";
/*cout << inside([0, 1]) << "\n";
cout << inside([1, 0]) << "\n";
cout << inside([0, 0]) << "\n";*/
}
void reset(int r, int c){
for(int i = 1; i <= r; i ++){
for(int j = 1; j <= c; j ++){
m[i][j] = 0;
}
}
}
int main(){
int r, c;
cin >> r >> c;
cin.get();
char ch;
vector <pair <int, int>> v;
pair <int, int> start;
pair <int, int> end;
for(int i = 1; i <= r; i ++){
for(int j = 1; j <= c; j ++){
ch = cin.get();
if(ch == '\n'){
break;
}
a[i][j] = ch;
if(a[i][j] == 'D'){
v.push_back({i, j});
}
else if(a[i][j] == 'I'){
start.first = i;
start.second = j;
}
else if(a[i][j] == 'O'){
end.first = i;
end.second = j;
}
}
cin.get();
}
dragonlee(r, c, v);
for(auto elem : v){
dist[elem.first][elem.second] = 0;
}
int st = 0, dr = r + c, sol = -1;
while(st <= dr){
int mij = (st + dr) / 2;
reset(r, c);
lee(start, mij, r, c);
if(m[end.first][end.second] > 0){
st = mij + 1;
sol = mij;
}
else {
dr = mij - 1;
}
}
cout << sol;
}