#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long longusing namespace std;const int N = 2000 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);int n, h, x[N], lft[N], rgt[N];
double ans, p, pr, pl;
double f[N][N][2][2];
bool vis[N][N][2][2];double dp(int i, int j, int u, int v) {if(i > j) return 0;if(vis[i][j][u][v]) return f[i][j][u][v];double& ans = f[i][j][u][v];double tmp1 = 0, tmp2 = 0;if(!u) ans += 0.5 * pl * (dp(i + 1, j, 0, v) + min(h, x[i] - x[i - 1])), tmp1 = min(h, x[i] - x[i - 1]);else ans += 0.5 * pl * (dp(i + 1, j, 0, v) + min(h, x[i] - x[i - 1] - h)), tmp1 = min(h, x[i] - x[i - 1] - h);if(v) ans += 0.5 * pr * (dp(i, j - 1, u, 1) + min(h, x[j + 1] - x[j])), tmp2 = min(h, x[j + 1] - x[j]);else ans += 0.5 * pr * (dp(i, j - 1, u, 1) + min(h, x[j + 1] - h - x[j])), tmp2 = min(h, x[j + 1] - h - x[j]);int L = min(rgt[i], j), R = max(lft[j], i);ans += 0.5 * pr * (dp(L + 1, j, 1, v) + x[L] - x[i] + (L != j ? h : tmp2));ans += 0.5 * pl * (dp(i, R - 1, u, 0) + x[j] - x[R] + (R != i ? h : tmp1));vis[i][j][u][v] = true;return ans;
}int main() {scanf("%d%d%lf", &n, &h, &p);pl = p, pr = 1 - p;for(int i = 1; i <= n; i++) scanf("%d", &x[i]);x[0] = -inf, x[n + 1] = inf;sort(x + 1, x + 1 + n);lft[1] = 1, rgt[n] = n;for(int i = 2; i <= n; i++)lft[i] = x[i] - h < x[i - 1] ? lft[i - 1] : i;for(int i = n - 1; i >= 1; i--)rgt[i] = x[i] + h > x[i + 1] ? rgt[i + 1] : i;printf("%.10f\n", dp(1, n, 0, 1));return 0;
}/*
*/