#include <iostream>
#include <fstream>
#include <deque>
using namespace std;

int dx[]={-1, 1, 0, 0};
int dy[]={0, 0, -1, 1};
char mat[1003][1003];
int r, c;

int BFSdragon(int startx, int starty) {
    /**
    deque<pair<int, int> > Q;
    int ok=0, i, j, d, x, y, p, q, min=10000;
    for(i=1; i<=r; i++) {
         for(j=1; j<=c; j++) {
              viz[i][j]=0;
         }
    }
    //verificare
    viz[startx][starty]=1;
    Q.push_back(make_pair(startx, starty));
    while(!Q.empty()) {
         x=Q.front().first;
         y=Q.front().second;
         for(i=0; i<4; i++) {
              p=x+dx[i];
              q=y+dy[i];
              if(viz[p][q]==0 && (mat[p][q]=='.' || mat[p][q]=='O')) {
                   viz[p][q]=viz[x][y]+1;
                   Q.push_back(make_pair(p, q));
              }
              if(mat[p][q]=='D') {
                   if(viz[x][y]+1<min) { min=viz[x][y]+1; }
              }
         }
         Q.pop_front();
    }
    return min;     
    **/
    //pastrez startx
    int min=10000, i, d=10000;
    if(mat[startx][starty]=='D') { return 0; }
    for(i=starty-1; i>=1; i--) {
         if(mat[startx][i]=='*') { break; }
         if(mat[startx][i]=='D') {
              d=starty-i;
              if(d<min) { min=d; }
              break;
         }
    }
    for(i=starty+1; i<=c; i++) {
         if(mat[startx][i]=='*') { break; }
         if(mat[startx][i]=='D') {
              d=i-starty;
              if(d<min) { min=d; }
              break;
         }
    }
    //pastrez starty
    for(i=startx-1; i>=1; i--) {
         if(mat[i][starty]=='*') { break; }
         if(mat[i][starty]=='D') {
              d=startx-i;
              if(d<min) { min=d; }
              break;
         }
    }
    for(i=startx+1; i<=r; i++) {
         if(mat[i][starty]=='*') { break; }
         if(mat[i][starty]=='D') {
              d=i-startx;
              if(d<min) { min=d; }
              break;
         }
    }
    return min;         
}

int BFS(int startx, int starty, int endx, int endy, int dist) {
    //dist = distanta minima pina la dragon ( > )
    deque<pair<int, int> > Q;
    int ok=0, i, j, d, x, y, p, q, mini;
    char viz[1002][1002];
    for(i=1; i<=r+1; i++) {
         for(j=1; j<=c+1; j++) {
              viz[i][j]=0;
         }
    }
    //verificare
    viz[startx][starty]=1;
    Q.push_back(make_pair(startx, starty));
    while(!Q.empty()) {
         x=Q.front().first;
         y=Q.front().second;
         for(i=0; i<4; i++) {
              ok=0;
              p=x+dx[i];
              q=y+dy[i];
              mini=BFSdragon(p, q);
              if(mini<dist) { ok=1; }
              if(ok==0 && viz[p][q]==0 && (mat[p][q]=='D' || mat[p][q]=='.' || mat[p][q]=='O')) {
                   if(p==endx && q==endy) {
                        return 1;
                   }
                   viz[p][q]=1;
                   Q.push_back(make_pair(p, q));   
              }
         }
         Q.pop_front();
    }                
    if(ok==1) { return 0; }
}

int cautabinar(int startx, int starty, int endx, int endy, int st, int dr) {
    int mij, q;
    while(st<=dr) {
        mij=st+(dr-st)/2;
        q=BFS(startx, starty, endx, endy, mij);
        if(q==0) { dr=mij-1; }
        else {
             if(BFS(startx, starty, endx, endy, mij+1)==1) { 
                  st=mij+1; 
             }
             else { return mij; }
        }
    }
    return -1;
}

int main() {
    FILE *in=fopen("barbar.in", "r"), *out=fopen("barbar.out", "w");
    int i, j, k, p, startx, starty, endx, endy;
    //r linii, c coloane
    fscanf(in, "%d%d\n", &r, &c);
    for(i=1; i<=r; i++) {
         for(j=1; j<=c; j++) {
              fscanf(in, "%c", &mat[i][j]);
              if(mat[i][j]=='I') { startx=i; starty=j; }
              if(mat[i][j]=='O') { endx=i; endy=j; }
         }
         fscanf(in, "\n");
    }
    for(i=0; i<=r; i++) {
         mat[0][i]='X'; mat[c+1][i]='X';
    }
    for(i=0; i<=c; i++) {
         mat[i][0]='X'; mat[i][r+1]='X';
    }
    mat[r+1][c+1]='X';
    //fprintf(out, "%d\n", cautabinar(startx, starty, endx, endy, 0, 1001));
    long bl=0,br=r*c,bm;
    while (br-bl>1)
    {
        bm=(bl+br)>>1;
        if (BFS(startx, starty, endx, endy, bm)) bl=bm;
        else br=bm;
    }
    if (bl) fprintf(out, "%ld\n",bl);
    else 
     if(BFS(startx, starty, endx, endy, 0)) { fprintf(out, "0\n"); }
     else { fprintf(out, "-1\n"); }
    fclose(in); fclose(out);
    //getch();
    return 0;
}