#include <iostream>
#include <fstream>
#include <queue>

using namespace std;

const int NMAX = 1005;

int a[NMAX][NMAX];
int d[NMAX][NMAX];
bool accesibil[NMAX][NMAX];
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, 1, 0, -1};

int n, m;

queue <pair <int, int> > q;

void bfs()
{
    while(!q.empty())
    {
        pair <int, int> p =q.front();
        q.pop();

        int x = p.first;
        int y = p.second;

        for(int i = 0; i < 4; i++)
        {
            int nx = x + dx[i];
            int ny = y + dy[i];

            if(d[nx][ny] == -1)
            {
                d[nx][ny] = d[x][y] + 1;
                q.push({nx, ny});
            }
        }
    }
}

bool exista_drum(int dist, pair<int, int> xs, pair <int, int> xf)
{
    if(d[xs.first][xs.second] < dist)
        return false;

    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
        {
            accesibil[i][j] = true;
            if(d[i][j] < dist)
                accesibil[i][j] = false;
        }

    queue <pair <int, int> > q2;

    q2.push(xs);

    while(!q2.empty())
    {
        pair <int, int> p = q2.front();
        q2.pop();

        for(int i = 0; i < 4; i++)
        {
            int x = p.first + dx[i];
            int y = p.second + dy[i];

            if(accesibil[x][y])
            {
                if(x == xf.first && y == xf.second)
                    return true;
                q2.push({x, y});
                accesibil[x][y] = false;
            }
        }
    }
    return false;
}

int caut_bin(pair <int, int> xs, pair <int, int> xf)
{
    int st, dr;
    st = 0;
    dr =  n * m;

    int rasp = -1;
    while(st <= dr)
    {
        int mij = (st + dr) / 2;
        if(exista_drum(mij, xs, xf))
        {
            rasp = mij;
            st = mij + 1;
        }else
            dr = mij - 1;

    }

    return rasp;
}

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


    fin >> n >> m;

    for(int i = 0; i <= n + 1; i++)
        d[i][0] = d[i][m + 1] = -2;
    for(int i = 0; i <= m + 1; i++)
        d[0][i] = d[n + 1][i] = -2;

    int xs, ys, xf, yf;
    xs = ys = xf = yf = 0;
    for(int i = 1; i <= n; i++)
    {
        string s;
        fin >> s;
        for(int j = 1; j <= m; j++)
        {
            if(s[j - 1] == '.')
                a[i][j] = -1;
            else if(s[j - 1] == '*')
                a[i][j] = -2;
            else if(s[j - 1] == 'D')
            {
                a[i][j] = 0;
                q.push({i, j});
            }else if(s[j - 1] == 'I')
            {
                a[i][j] = -1;
                xs = i;
                ys = j;
            }else
            {
                a[i][j] = -1;
                xf = i;
                yf = j;
            }
        }
    }

    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= m; j++)
            d[i][j] = a[i][j];

    bfs();

    fout << caut_bin({xs, ys}, {xf, yf});

    return 0;
}