#include <bits/stdc++.h>
using namespace std;
const long long N = 1010;
char s[N][N], tmp[N][N];
long long cntr1[N], sumr1[N], cntr2[N], sumr2[N], cntc1[N], cntc2[N], sumc1[N],
    sumc2[N];
long long lf[N], rt[N], ans = 0, n, m;
void sol(long long *l, long long *r) {
  long long now = 0;
  for (long long i = 1; i <= n; i++) {
    if (l[i] == -1) continue;
    if (l[i - 1] == -1 || l[i] < l[i - 1]) now = 0;
    ans += 2 * now * r[i];
    ans += l[i] * r[i];
    now += l[i];
  }
}
void rvs() {
  for (long long i = 1; i <= n / 2; i++)
    for (long long j = 1; j <= m; j++) swap(s[i][j], s[n - i + 1][j]);
}
void Sol() {
  for (long long i = 1; i <= n; i++) lf[i] = rt[i] = -1;
  for (long long i = 1; i <= n; i++)
    for (long long j = 1; j <= m; j++)
      if (s[i][j] == 'X') lf[i] = j - 1, rt[i] = m - j;
  sol(lf, rt);
  sol(rt, lf);
}
signed main() {
  scanf("%lld%lld", &n, &m);
  for (long long i = 1; i <= n; i++) scanf("%s", s[i] + 1);
  long long tot = 0;
  for (long long i = 1; i <= n; i++)
    for (long long j = 1; j <= m; j++) tot += s[i][j] == '.';
  for (long long i = 1; i <= n; i++) {
    cntr1[i] = cntr1[i - 1];
    sumr1[i] = sumr1[i - 1];
    for (long long j = 1; j <= m; j++)
      if (s[i][j] == '.') cntr1[i]++, sumr1[i] += i;
  }
  for (long long i = n; i; i--) {
    cntr2[i] = cntr2[i + 1];
    sumr2[i] = sumr2[i + 1];
    for (long long j = 1; j <= m; j++)
      if (s[i][j] == '.') cntr2[i]++, sumr2[i] += i;
  }
  for (long long j = 1; j <= m; j++) {
    cntc1[j] = cntc1[j - 1];
    sumc1[j] = sumc1[j - 1];
    for (long long i = 1; i <= n; i++)
      if (s[i][j] == '.') cntc1[j]++, sumc1[j] += j;
  }
  for (long long j = m; j; j--) {
    cntc2[j] = cntc2[j + 1];
    sumc2[j] = sumc2[j + 1];
    for (long long i = 1; i <= n; i++)
      if (s[i][j] == '.') cntc2[j]++, sumc2[j] += j;
  }
  for (long long i = 1; i <= n; i++) {
    for (long long j = 1; j <= m; j++) {
      if (s[i][j] == 'X') continue;
      long long sum = 0;
      sum += i * cntr1[i - 1] - sumr1[i - 1];
      sum += sumr2[i + 1] - i * cntr2[i + 1];
      sum += j * cntc1[j - 1] - sumc1[j - 1];
      sum += sumc2[j + 1] - j * cntc2[j + 1];
      ans += sum;
    }
  }
  Sol();
  rvs();
  Sol();
  for (long long i = 1; i <= n; i++)
    for (long long j = 1; j <= m; j++) tmp[j][i] = s[i][j];
  swap(n, m);
  for (long long i = 1; i <= n; i++)
    for (long long j = 1; j <= m; j++) s[i][j] = tmp[i][j];
  Sol();
  rvs();
  Sol();
  printf("%.6lf", (double)ans / tot / tot);
  return 0;
}
