#include<cstdio>
#include<cstring>
#include<cmath>
#include<ctime>
#include<string>
#include<vector>
#include<queue>
#include<deque>
#include<set>
#include<list>
#include<stack>
#include<bitset>
#include<algorithm>
#define INF (1 << 30)
#define pb push_back
#define mkp make_pair
#define pii pair<int, int>
#define ll long long
#define nxt (*it)
#define x first
#define y second
#define type int
#define FOR(i,a,b)\
   for(int i=a; i<=b; ++i)
#define FORR(i,a,b)\
   for(int i=a; i>=b; --i)
#define ALLR(g) \
   for(typeof(g.rbegin()) it=g.rbegin(); it!=g.rend(); ++it)
#define ALL(g)\
   for(typeof(g.begin()) it=g.begin(); it!=g.end(); ++it)
#define infile "barbar.in"
#define outfile "barbar.out"
#define nMax 1005
using namespace std;

 queue < pii > Q;

 pii iPos, fPos;

 int A[nMax][nMax];

 bool OK[nMax][nMax];

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

int N, M, Dmax, Sol = -1;

 void init(){
     FOR(i,1,N)
        FOR(j,1,M)
             A[i][j] = -INF;
 }

void read(){
    freopen(infile, "r", stdin);

    scanf("%d %d", &N, &M);

    init();

    char c;
    FOR(i,1,N){
        getchar();
        FOR(j,1,M){
            scanf("%c", &c);

            switch(c){
                case 'I':{iPos = mkp(i,j);
                }break;
               case 'D':{Q.push(mkp(i,j));
               A[i][j] = 0;
               } break;
               case '*':{A[i][j] = -1;
               }break;
               case 'O':{fPos = mkp(i,j);
               }break;
            }
        }
    }

    fclose(stdin);
}

 inline bool inMatrix(const pii &p){
     if(p.x >= 1 && p.x <= N && p.y >= 1 && p.y <= M)
          return true;
    return false;
 }

 void BFS(){
     while(!Q.empty()){
          pii nod = Q.front();
          Q.pop();

          Dmax = max(Dmax, A[nod.x][nod.y]);

          FOR(i,0,3){
              pii next = mkp(nod.x + dx[i], nod.y + dy[i]);
              if(!inMatrix(next)|| (A[next.x][next.y] != -INF && A[next.x][next.y]  <= A[nod.x][nod.y] + 1))
                   continue;
             A[next.x][next.y] = A[nod.x][nod.y] + 1;
             Q.push(next);
          }
     }
 }

 bool isPath(int d){
     FOR(i,1,N)
        FOR(j,1,M)
           OK[i][j] = false;

     if(A[iPos.x][iPos.y] < d)
        return false;

     OK[iPos.x][iPos.y] = true;
     Q.push(iPos);

     while(!Q.empty()){
        pii nod = Q.front();
        Q.pop();

        FOR(i,0,3){
            pii next = mkp(nod.x + dx[i], nod.y + dy[i]);
            if(!inMatrix(next)|| OK[next.x][next.y] || A[next.x][next.y]  < d)
                continue;

            OK[next.x][next.y] = true;
            Q.push(next);
        }
     }

     return (OK[fPos.x][fPos.y] == true);
 }

void search(int l, int r){
    while(l <= r){
        int m = (l + r) >> 1;
        if(isPath(m)){
            Sol = m;
            l = m + 1;
        }
        else
            r = m - 1;
    }
}

void print(){
    freopen(outfile, "w", stdout);

    printf("%d\n", Sol);

    fclose(stdout);
}

int main(){
    read();

    BFS();
    search(0, Dmax);

    print();

    return 0;
}