#include <bits/stdc++.h>
#pragma GCC optimize("O3")
using namespace std;
int in() {
  int x;
  cin >> x;
  return x;
}
long long lin() {
  long long x;
  cin >> x;
  return x;
}
string stin() {
  string s;
  cin >> s;
  return s;
}
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
vector<int> iota(int n) {
  vector<int> a(n);
  iota(begin(a), end(a), 0);
  return a;
}
void print() { putchar(' '); }
void print(bool a) { cout << a; }
void print(int a) { cout << a; }
void print(long long a) { cout << a; }
void print(char a) { cout << a; }
void print(string& a) { cout << a; }
void print(double a) { cout << a; }
template <class T>
void print(const vector<T>&);
template <class T, size_t size>
void print(const array<T, size>&);
template <class T, class L>
void print(const pair<T, L>& p);
template <class T, size_t size>
void print(const T (&)[size]);
template <class T>
void print(const vector<T>& a) {
  if (a.empty()) return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    cout << " ";
    print(*i);
  }
  cout << endl;
}
template <class T>
void print(const deque<T>& a) {
  if (a.empty()) return;
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    cout << " ";
    print(*i);
  }
}
template <class T, size_t size>
void print(const array<T, size>& a) {
  print(a[0]);
  for (auto i = a.begin(); ++i != a.end();) {
    cout << " ";
    print(*i);
  }
}
template <class T, class L>
void print(const pair<T, L>& p) {
  cout << '(';
  print(p.first);
  cout << ",";
  print(p.second);
  cout << ')';
}
template <class T, size_t size>
void print(const T (&a)[size]) {
  print(a[0]);
  for (auto i = a; ++i != end(a);) {
    cout << " ";
    print(*i);
  }
}
template <class T>
void print(const T& a) {
  cout << a;
}
int out() {
  putchar('\n');
  return 0;
}
template <class T>
int out(const T& t) {
  print(t);
  putchar('\n');
  return 0;
}
template <class Head, class... Tail>
int out(const Head& head, const Tail&... tail) {
  print(head);
  putchar(' ');
  out(tail...);
  return 0;
}
long long gcd(long long a, long long b) {
  while (b) {
    long long c = b;
    b = a % b;
    a = c;
  }
  return a;
}
long long lcm(long long a, long long b) {
  if (!a || !b) return 0;
  return a * b / gcd(a, b);
}
vector<pair<long long, long long>> factor(long long x) {
  vector<pair<long long, long long>> ans;
  for (long long i = 2; i * i <= x; i++)
    if (x % i == 0) {
      ans.push_back({i, 1});
      while ((x /= i) % i == 0) ans.back().second++;
    }
  if (x != 1) ans.push_back({x, 1});
  return ans;
}
vector<int> divisor(int x) {
  vector<int> ans;
  for (int i = 1; i * i <= x; i++)
    if (x % i == 0) {
      ans.push_back(i);
      if (i * i != x) ans.push_back(x / i);
    }
  return ans;
}
template <class T>
void UNIQUE(vector<T>& x) {
  sort(begin(x), end(x));
  x.erase(unique(begin(x), end(x)), x.end());
}
int popcount(long long x) { return __builtin_popcountll(x); }
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int n) { return uniform_int_distribution<int>(0, n)(rng); }
template <class... T>
void err(const T&...) {}
bool dp[10100][1010];
signed main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cout << fixed << setprecision(15);
  int m = in(), n = in();
  vector<int> a;
  for (long long i = 0; i < n; i++) a.push_back(in());
  UNIQUE(a);
  n = a.size();
  int g = in(), r = in();
  for (long long i = 0; i < n; i++) dp[i][0] = 1;
  for (long long j = 0; j < g + 1; j++) dp[n - 1][j] = 1;
  for (long long j = 0; j < g + 1; j++) {
    for (long long i = 0; i < n; i++) {
      if (i and j >= a[i] - a[i - 1]) {
        dp[i][j] |= dp[i - 1][j - a[i] + a[i - 1]];
      }
      if (i != n - 1 and j >= a[i + 1] - a[i]) {
        dp[i][j] |= dp[i + 1][j - a[i + 1] + a[i]];
      }
    }
  }
  if (!dp[0][g]) {
    cout << -1 << '\n';
    return 0;
  }
  queue<pair<int, int>> q;
  q.emplace(0, g);
  int t = 0;
  vector<vector<bool>> used(n, vector<bool>(g + 1));
  used[0][g] = 1;
  long long ans = LONG_LONG_MAX;
  while (!q.empty()) {
    queue<pair<int, int>> nxt;
    while (!q.empty()) {
      auto [pl, s] = q.front();
      q.pop();
      if (pl == n - 1) {
        chmin(ans, (long long)t * (r + g) + g - s);
      }
      if (pl) {
        int D = a[pl] - a[pl - 1];
        if (s >= D and !used[pl - 1][s - D] and dp[pl - 1][s - D]) {
          q.emplace(pl - 1, s - D);
          used[pl - 1][s - D] = 1;
        }
      }
      if (pl != n - 1) {
        int D = a[pl + 1] - a[pl];
        if (s >= D and !used[pl + 1][s - D] and dp[pl + 1][s - D]) {
          q.emplace(pl + 1, s - (a[pl + 1] - a[pl]));
          used[pl + 1][s - D] = 1;
        }
      }
      if (dp[pl][g - s]) nxt.emplace(pl, g - s);
    }
    while (!nxt.empty()) {
      auto p = nxt.front();
      nxt.pop();
      if (!used[p.first][p.second]) {
        used[p.first][p.second] = 1;
        q.emplace(p);
      }
    }
    t++;
  }
  if (ans == LONG_LONG_MAX) {
    cout << -1 << '\n';
  } else
    cout << ans << '\n';
}
