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

int dx[]={-1, 1, 0, 0};
int dy[]={0, 0, -1, 1};
char mat[1002][1002];
int r, c, viz[1002][1002];

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;         
}

int BFS(int startx, int starty, int endx, int endy, int dist) {
    //dist = distanta minima pina la dragon ( > )
    deque<pair<int, int> > Q;
    int viz[500][500], ok=0, i, j, d, x, y, p, q, mini;
    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++) {
              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]=='.' || 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 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';
    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 fprintf(out, "-1\n");
    fclose(in); fclose(out);
    return 0;
}