#include <bits/stdc++.h>
using namespace std;
const int N = 2005;
int n, h;
double p;
int a[N], f[N], b[N];
double dp[N][N][2][2];
double f1(int l, int r, int d1, int d2) {
  if (l > r) return 0;
  if (dp[l][r][d1][d2] != -1) return dp[l][r][d1][d2];
  double &res = dp[l][r][d1][d2];
  res = 0;
  if (d1 == -1)
    res += p * (f1(l + 1, r, 0, d2) + h);
  else if (d1 == 1) {
    res += p * (f1(l + 1, r, 0, d2) + min(h, (a[l] - a[l - 1] - h)));
  } else {
    res += p * (f1(l + 1, r, 0, d2) + min(h, a[l] - a[l - 1]));
  }
  int idx = l + f[l] - 1, tot = a[min(r, idx)] - a[l];
  if (idx >= r) {
    if (d2 == -1) {
      tot += h;
    } else if (d2 == 1) {
      tot += min(h, a[r + 1] - a[r]);
    } else {
      tot += min(h, a[r + 1] - a[r] - h);
    }
    res += (1 - p) * tot;
  } else {
    tot += h;
    res += (1.0 - p) * (f1(l + f[l], r, 1, d2) + tot);
  }
  idx = r - b[r] + 1, tot = a[r] - a[max(l, idx)];
  if (idx <= l) {
    if (d1 == -1) {
      tot += h;
    } else if (d1 == 1) {
      tot += min(h, a[l] - a[l - 1] - h);
    } else {
      tot += min(h, a[l] - a[l - 1]);
    }
    res += p * tot;
  } else {
    tot += h;
    res += p * (f1(l, r - b[r], d1, 0) + tot);
  }
  if (d2 == -1) {
    res += (1.0 - p) * (f1(l, r - 1, d1, 1) + h);
  } else if (d2 == 0) {
    res += (1.0 - p) * (f1(l, r - 1, d1, 1) + min(h, a[r + 1] - a[r] - h));
  } else {
    res += (1.0 - p) * (f1(l, r - 1, d1, 1) + min(h, a[r + 1] - a[r]));
  }
  res /= 2;
  return res;
}
int main() {
  cin >> n >> h >> p;
  for (int i = 0; i < (int)(n); ++i) {
    cin >> a[i];
  }
  a[n] = -500000000;
  a[n + 1] = 500000000;
  n += 2;
  sort(a, a + n);
  b[0] = 1;
  for (int i = 1; i < n; i++) {
    if (a[i] - h < a[i - 1]) {
      b[i] = b[i - 1] + 1;
    } else {
      b[i] = 1;
    }
  }
  f[n - 1] = 1;
  for (int i = n - 2; i >= 0; i--) {
    if (a[i] + h > a[i + 1]) {
      f[i] = f[i + 1] + 1;
    } else {
      f[i] = 1;
    }
  }
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
      for (int k = 0; k < (int)(2); ++k)
        for (int l = 0; l < (int)(2); ++l) dp[i][j][k][l] = -1.0;
    }
  }
  double ans = f1(1, n - 2, 0, 1);
  printf("%.9lf", ans);
  return 0;
}
