#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define fi first
#define se second
#define pp push_back
#define all(x) (x).begin(), (x).end()
#define Ones(n) __builtin_popcount(n)
#define endl '\n'
#define mem(arrr, xx) memset(arrr,xx,sizeof arrr)
//#define int long long
#define debug(x) cout << (#x) << " = " << x << endl

void Gamal() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef Clion
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

int dx[] = {+0, +0, -1, +1, +1, +1, -1, -1};
int dy[] = {-1, +1, +0, +0, +1, -1, +1, -1};

const double EPS = 1e-9;
const ll OO = 0X3F3F3F3F3F3F3F3F;
const int N = 2e5 + 5, INF = INT_MAX, MOD = 1e9 + 7, LOG = 20;


void solve() {
    int n, l, r;
    cin >> n >> l >> r;
    vector<ll> v(n);
    for (int i = 0; i < n; ++i) {
        cin >> v[i];
    }
    sort(all(v));
    vector<ll> mx(n,r);
    for (int i = 0; i < n; ++i) {
        if(i)mx[i] = min(mx[i],2 * (v[i] - v[i - 1]));
        if (i != n - 1)mx[i] = min(mx[i], 2 * (v[i + 1] - v[i]));
    }
    ll ans = 0;
    for (int i = 0; i < n; ++i) {
        if (i != n - 1 && mx[i + 1] >= l) {
            // x  <= 2 * v[i + 1] - 2 * v[i] - l
            ll x = 2 * v[i + 1] - 2 * v[i] - l;
            if (x >= l)mx[i] = min(mx[i], x);
        }
        if (mx[i] >= l) {
            ans += mx[i];
            if (i != n - 1) {
                // v[i + 1] - v[i] + mx[i] >=  x
                mx[i + 1] = min(mx[i + 1], 2 * (v[i + 1] - v[i]) - mx[i]);
            }
        }
    }
    if(ans == 0)ans = -1;
    cout << ans;
}


signed main() {
    Gamal();
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}