#include <bits/stdc++.h>
using namespace std;
int n, h, x[2010], fall[2][2010];
double p, dp[2010][2010][2][2];
double solve(int l, int r, int fl, int fr) {
  if (l > r) return 0;
  if (dp[l][r][fl][fr] != -1) return dp[l][r][fl][fr];
  dp[l][r][fl][fr] = 0;
  double res = 0;
  int nl = min(r, l + fall[0][l] - 1);
  if (nl == r) {
    if (!fr)
      res += (1 - p) * (x[r] - x[l] + min(h, x[r + 1] - x[r] - h));
    else
      res += (1 - p) * (x[r] - x[l] + min(h, x[r + 1] - x[r]));
  } else {
    res += (1 - p) * solve(nl + 1, r, 1, fr);
    res += (1 - p) * (x[nl] - x[l] + h);
  }
  if (fl)
    res += p * min(h, x[l] - x[l - 1] - h);
  else
    res += p * min(h, x[l] - x[l - 1]);
  res += p * solve(l + 1, r, 0, fr);
  int nr = max(l, r - fall[1][r] + 1);
  if (nr == l) {
    if (fl)
      res += p * (x[r] - x[l] + min(h, x[l] - x[l - 1] - h));
    else
      res += p * (x[r] - x[l] + min(h, x[l] - x[l - 1]));
  } else {
    res += p * solve(l, nr - 1, fl, 0);
    res += p * (x[r] - x[nr] + h);
  }
  if (!fr)
    res += (1 - p) * min(h, x[r + 1] - x[r] - h);
  else
    res += (1 - p) * min(h, x[r + 1] - x[r]);
  res += (1 - p) * solve(l, r - 1, fl, 1);
  res /= 2;
  return dp[l][r][fl][fr] = res;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(NULL);
  cin >> n >> h >> p;
  for (int i = (1); i <= (n); i++) cin >> x[i];
  x[++n] = 1000000000;
  x[++n] = -1000000000;
  sort(x + 1, x + n + 1);
  fall[1][1] = 1;
  for (int i = (2); i <= (n); i++) {
    if (x[i] - x[i - 1] < h)
      fall[1][i] = fall[1][i - 1] + 1;
    else
      fall[1][i] = 1;
  }
  fall[0][n] = 1;
  for (int i = (n - 1); i >= (1); i--) {
    if (x[i + 1] - x[i] < h)
      fall[0][i] = fall[0][i + 1] + 1;
    else
      fall[0][i] = 1;
  }
  for (int i = (1); i <= (n); i++)
    for (int j = (1); j <= (n); j++)
      for (int k = (0); k <= (1); k++)
        for (int l = (0); l <= (1); l++) dp[i][j][k][l] = -1;
  cout << fixed << setprecision(9) << solve(2, n - 1, 0, 1);
  return 0;
}
