#include <fstream>
#include <queue>
#define NMAX 1000

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

struct punct{
    int x, y;
};
queue <punct> q;
queue <punct> que;

int a[NMAX + 2][NMAX + 2];
int dist[NMAX + 2][NMAX + 2];
int viz[NMAX + 2][NMAX + 2];

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

int main()
{
    int n, m, st, dr, mij;
    char x;
    punct aux, nou, barbar, dragon;
    fin >> n >> m;
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++){
            fin >> x;
            if(x == 'D'){
                a[i][j] = -1;
                que.push(dragon);
            }
            else if(x == '*')
                a[i][j] = -2;
            else if(x == 'I'){
                barbar.x = i;
                barbar.y = j;
                q.push(barbar);
                viz[i][j] = 1;
            }
    }
    for(int i = 1; i <= n; i++)
        a[i][0] = a[i][n + 1] = -2;
    for(int j = 1; j <= n; j++)
        a[0][j] = a[n + 1][j] = -2;

    while(!q.empty()){
        aux = q.front();
        for(int dir = 0; dir < 4; dir++){
            nou.x = aux.x + dx[dir];
            nou.y = aux.y + dy[dir];
            if(a[nou.x][nou.y] == 0 && viz[nou.x][nou.y] != 1){
                viz[nou.x][nou.y] = 1;
                dist[nou.x][nou.y] = dist[aux.x][aux.y] + 1;
                a[nou.x][nou.y] = dist[nou.x][nou.y];
                q.push(nou);
            }
        }
        q.pop();
    }
    st = 1; dr = (n - 1)*(m - 1);
    while(st < dr){
        ok = 1;
       mij = (st + dr)/2;
       aux = que.front();
       for(int dir = 0; dir < 4; dir++){
            nou.x = aux.x;
            nou.y = aux.y;
            if(dir < 2){
                nou.x += mij;
                nou.y += mij;
            }else{
                nou.x -= mij;
                nou.y -= mij;
            }
            if(a[nou.x][nou.y] == -2 || a[nou.x][nou.y] == -1){
                st = mij + 1;
            }else{
                dr = mij - 1;
                last = mij;
            }
        }
    }
    /*for(int i = 1; i <= n; i++){
        for(int j = 1; j <= m; j++)
            fout << a[i][j] << ' ';
        fout << '\n';*/
    }
    fout << last;
    return 0;
}