#include <fstream>
#include <queue>
using namespace std;

ifstream fin("barbar.in");
ofstream fout("barbar.out");

const int N = 1e3;
const int INIT = 1e9;
const int DIRS = 4;

char v[N+1][N+1];
int dragons[N+1][N+1];
int lee[N+1][N+1];

int dln[] = {-1,0,1,0};
int dcl[] = {0,-1,0,1};
void reset(int v[N+1][N+1], int nl, int nc){
    for (int i = 1; i<=nl; i++)
        for (int j = 1; j<=nc; j++)
            v[i][j]=INIT;
}
void golee(int lee[N+1][N+1], int ln, int cl, int nl, int nc, int k, bool avoid){
    queue<pair<int,int>> q;
    lee[ln][cl] = 0;
    q.push({ln,cl});

    while(!q.empty()){
        ln = q.front().first;
        cl = q.front().second;
        q.pop();

        if (lee[ln][cl]<k)
        for (int i = 0; i<4; i++){
            int fln = ln+dln[i];
            int fcl = cl+dcl[i];

            if (fln>0 && fln<=nl && fcl>0 && fcl<=nc && v[fln][fcl]!='*' &&
            lee[fln][fcl]>lee[ln][cl]+1 && (avoid == 0 || dragons[fln][fcl]==INIT)){
                lee[fln][fcl]=lee[ln][cl]+1;
                q.push({fln,fcl});
            }
        }
    }
}

bool sePoate(int k, int iln, int icl, int oln, int ocl, int nl, int nc){
    reset(dragons, nl, nc);
    reset(lee, nl, nc);
    for (int i = 1; i<=nl; i++){
        for (int j = 1; j<=nc; j++){
            if (v[i][j]=='D'){
                golee(dragons,i,j,nl,nc,k,0);
            }
        }
    }
    golee(lee,iln,icl,nl,nc,1e9,1);
    return (lee[oln][ocl]!=INIT);

}

int cb(int iln, int icl, int oln, int ocl, int nl, int nc){
    int st = 0, dr=max(nl,nc), rez = st-1;

    while (st<=dr){
        int m = (st+dr)/2;

        if (sePoate(m,iln,icl,oln,ocl,nl,nc)){
            rez = m;
            st = m+1;
        }
        else{
            dr = m-1;
        }
    }
    return rez;
}

int main(){
    int nl, nc;
    fin>>nl>>nc;

    int iln=0,icl=0,oln=0,ocl=0;

    for (int i = 1; i<=nl; i++){
        for (int j = 1; j<=nc; j++){
            fin>>v[i][j];
            if (v[i][j]=='I'){
                iln = i;
                icl = j;
            }
            if (v[i][j]=='O'){
                oln=i;
                ocl=j;
            }
        }
    }

    int sol = cb(iln,icl,oln,ocl,nl,nc)+1;
    if (sol == 0)
    fout<<-1;
    else
    fout<<sol;

    
}