#include <bits/stdc++.h>
using namespace std;
char mp[1050][1050];
int hang[1050], lie[1050];
int cnt, n, m;
long long tot;
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; ++i) {
    scanf(" %s", mp[i] + 1);
    for (int j = 1; j <= m; ++j)
      if (mp[i][j] == 'X')
        hang[i] = j, lie[j] = i;
      else
        cnt++;
  }
  for (int i = 1; i <= n; ++i)
    for (int j = i + 1; j <= n; ++j)
      tot += (m - (hang[i] > 0)) * (m - (hang[j] > 0)) * 2 * 1ll * (j - i);
  for (int i = 1; i <= m; ++i)
    for (int j = i + 1; j <= m; ++j)
      tot += (n - (lie[i] > 0)) * (n - (lie[j] > 0)) * 2 * 1ll * (j - i);
  for (int i = 1; i <= n; ++i)
    if (hang[i]) tot += 2 * 2 * (hang[i] - 1) * (m - hang[i]);
  for (int i = 1; i <= m; ++i)
    if (lie[i]) tot += 2 * 2 * (lie[i] - 1) * (n - lie[i]);
  int cur = 0;
  int way = 0;
  for (int i = 1; i <= n; ++i) {
    if (hang[i]) {
      if (way == 1)
        tot += 2 * 2 * 1ll * cur * (hang[i] - 1);
      else
        tot += 2 * 2 * 1ll * cur * (m - hang[i]);
      if (hang[i + 1]) {
        if (way == 0) {
          if (hang[i + 1] > hang[i])
            cur += hang[i] - 1;
          else
            way = 1, cur = m - hang[i];
        } else {
          if (hang[i + 1] < hang[i])
            cur += m - hang[i];
          else
            way = 0, cur = hang[i] - 1;
        }
      } else
        cur = 0;
    } else
      cur = 0;
  }
  cur = 0, way = 0;
  for (int i = 1; i <= m; ++i) {
    if (lie[i]) {
      if (way == 1)
        tot += 2 * 2 * 1ll * cur * (lie[i] - 1);
      else
        tot += 2 * 2 * 1ll * cur * (n - lie[i]);
      if (lie[i + 1]) {
        if (way == 0) {
          if (lie[i + 1] > lie[i])
            cur += lie[i] - 1;
          else
            way = 1, cur = n - lie[i];
        } else {
          if (lie[i + 1] < lie[i])
            cur += n - lie[i];
          else
            way = 0, cur = lie[i] - 1;
        }
      } else
        cur = 0;
    } else
      cur = 0;
  }
  printf("%.12lf\n", tot * 1.00 / cnt * 1.00 / cnt * 1.00);
}
