#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#include <cstdio>
#include <numeric>
#include <cmath>
#include <assert.h>
#include <deque>
#include <iostream>
#include <queue>
#include <string.h>
#include <set>
#include <algorithm>
#include <map>
#include <vector>
#include <bitset>
#include <array>
#define loop(i, n) for (int i = 0; i < n; i++)
#define testcase int _t; cin >> _t; while (_t--)
#define all(x) (x).begin(), (x).end()
using i64 = long long;
using namespace std;
 
void yes(bool y) {
  cout << (y ? "Yes\n" : "No\n");
}
 
template<typename T>
ostream& operator<<(ostream& os, vector<T> const &v) {
  for (T x: v) {
    os << x << ' ';
  }
  cout << '\n';
  return os;
}
 
template<typename T>
istream& operator>>(istream& is, vector<T> &v) {
  for (T &x: v) {
    is >> x;
  }
  return is;
}
 
const int maxn = 1e6;
 
int n, m, g, r;
vector<int> d;
bitset<int(1e4 * 2000 * 2)> vis;
 
inline auto idx(array<i64, 3> x) {
  return x[1] * (g + r) + x[2];
}
 
i64 bfs() {
  priority_queue< array<i64, 3> > q;
  q.push({0, 0, 0});
 
  while (!q.empty()) {
    auto tup = q.top(); q.pop();
    i64 &dist = tup[0];
    i64 &line = tup[1];
    i64 &secs = tup[2];
    auto i = idx(tup); 
 
    if (vis[i]) continue;
    vis[i] = 1;
 
    if (line == m - 1) {
      return dist;
    }
 
    if (secs == g) { // wait for next go
      int cost = r;
      array<i64, 3> nxt = {dist + cost, line, 0};
      q.push(nxt);
    }
    if (line + 1 < m) {
      int cost = d[line + 1] - d[line]; 
      if (secs + cost <= g) {
        array<i64, 3> nxt = {dist + cost, line + 1, secs + cost};
        q.push(nxt);
      }
    }
    if (line - 1 >= 0) {
      int cost = d[line] - d[line - 1]; 
      if (secs + cost <= g) {
        array<i64, 3> nxt = {dist + cost, line - 1, secs + cost};
        q.push(nxt);
      }
    }
  }
  return -1;
}
 
int main() {
  ios_base::sync_with_stdio(false); 
  cin.tie(NULL);
  cin >> n >> m;
  d.resize(m);
  cin >> d;
  cin >> g >> r;
  sort(all(d));
  cout << bfs() << '\n';
}

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