#include <bits/stdc++.h>
using namespace std;
int dis[10001][1001];
int pos[10001];
int g, r, n, m;
void bfs() {
  deque<pair<int, pair<int, int> > > fila;
  fila.push_front({0, {0, 0}});
  while (!fila.empty()) {
    int v = fila.front().first;
    int s = fila.front().second.first;
    int t = fila.front().second.second;
    fila.pop_front();
    if (dis[v][s] != -1) continue;
    dis[v][s] = t;
    if (v) {
      if (s < g and s + (pos[v] - pos[v - 1]) <= g and
          dis[v - 1][s + (pos[v] - pos[v - 1])] == -1) {
        fila.push_front({v - 1, {s + (pos[v] - pos[v - 1]), t}});
      }
    }
    if (v < m - 1) {
      if (s < g and s + (pos[v + 1] - pos[v]) <= g and
          dis[v + 1][s + (pos[v + 1] - pos[v])] == -1) {
        fila.push_front({v + 1, {s + (pos[v + 1] - pos[v]), t}});
      }
    }
    if (s == g and dis[v][0] == -1) {
      fila.push_back({v, {0, t + 1}});
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  memset(dis, -1, sizeof(dis));
  cin >> n >> m;
  int l[m];
  for (int i = 0; i < m; i++) cin >> l[i];
  sort(l, l + m);
  for (int i = 0; i < m; i++) pos[i] = l[i];
  cin >> g >> r;
  bfs();
  int res = -1;
  for (int i = 0; i < m - 1; i++) {
    if (dis[i][0] == -1) continue;
    if ((pos[m - 1] - pos[i]) > g) continue;
    int atual = dis[i][0] * (g + r) + (pos[m - 1] - pos[i]);
    if (res == -1)
      res = atual;
    else
      res = min(res, atual);
  }
  cout << res << endl;
}
