#include <cstdio>
#include <deque>

const int MAX_N = 1000;
char map[MAX_N + 2][MAX_N + 2];
int dist[MAX_N + 2][MAX_N + 2];
const int EMPTY = 1;
const int WALL = 0;
const int DRAGON = 2;
int dLin[] = {0, 1, 0,-1};
int dCol[] = {1, 0,-1, 0};

struct coord {
  int l, c, val;
};

int main() {
  int n, m, l, c, lIn, cIn, lOut, cOut, i, lN, cN, val;
  coord x;
  std::deque<coord> d;
  char ch;

  FILE *fin = fopen("barbar.in", "r");
  fscanf(fin, "%d%d", &n, &m);
  for(l = 1; l <= n; l++) {
    ch = fgetc(fin);
    while(ch != '\n')
      ch = fgetc(fin);
    for(c = 1; c <= m; c++) {
      ch = fgetc(fin);
      if(ch == '.')
        map[l][c] = EMPTY;
      else if(ch == 'D') {
        map[l][c] = WALL;
        x.l = l;
        x.c = c;
        x.val = 0;
        d.push_back(x);
      } else if(ch == '*')
        map[l][c] = WALL;
      else if(ch == 'I') {
        lIn = l;
        cIn = c;
        map[l][c] = EMPTY;
      } else {
        lOut = l;
        cOut = c;
        map[l][c] = EMPTY;
      }
    }
  }
  fclose(fin);

  while(d.size() > 0) {
    l = d.front().l;
    c = d.front().c;
    val = d.front().val;
    dist[l][c] = val;
    d.pop_front();
    for(i = 0; i < 4; i++) {
      lN = l + dLin[i];
      cN = c + dCol[i];
      x.l = lN;
      x.c = cN;
      x.val = val + 1;
      if(map[lN][cN] == EMPTY) {
        map[lN][cN] = WALL;
        d.push_back(x);
      }
    }
  }

  for(l = 0; l <= n + 1; l++)
    dist[l][0] = dist[l][m + 1] = 0;
  for(c = 0; c <= m + 1; c++)
    dist[0][c] = dist[n + 1][c] = 0;

  x.l = lIn;
  x.c = cIn;
  x.val = dist[lIn][cIn];
  d.push_back(x);
  dist[lIn][cIn] = 0;
  do {
    l = d.front().l;
    c = d.front().c;
    val = d.front().val;
    d.pop_front();
    for(i = 0; i < 4; i++) {
      x.l = lN = l + dLin[i];
      x.c = cN = c + dCol[i];
      if(dist[lN][cN] > 0) {
        if(dist[lN][cN] >= val) {
          x.val = val;
          d.push_front(x);
        } else {
          x.val = dist[lN][cN];
          d.push_back(x);
        }
        dist[lN][cN] = -1;
      }
    }
  } while((l != lOut || c != cOut) && d.size() > 0);

  FILE *fout = fopen("barbar.out", "w");
  if(l == lOut && c == cOut)
    fprintf(fout, "%d", val);
  else
    fprintf(fout, "-1");
  fclose(fout);
  return 0;
}