/// Msaa el 5ra
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")

#include "bits/stdc++.h"

using namespace std;

#define pb push_back
#define F first
#define S second
#define f(i, a, b)  for(int i = a; i < b; i++)
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x) (int)(x).size()
#define mp(x, y) make_pair(x,y)
#define popCnt(x) (__builtin_popcountll(x))
#define int ll

using ll = long long;
using ii = pair<int, int>;
using ull = unsigned long long;

const int N = 5e5 + 5, LG = 18, MOD = 1e9 + 7;
const long double PI = acos(-1);
const long double EPS = 1e-7;

void doWork() {

    int n, l, r;
    cin >> n >> l >> r;
    vector<ii> ranges;
    vector<int> vec(n);
    f(i, 0, n) {
        cin >> vec[i];
        vec[i] *= 2;
    }
    sort(all(vec));

    ranges.push_back({0, 0});
    f(i, 0, n) {
        int x = vec[i];
        if (ranges.empty() || ranges.back().S <= x - l)
            ranges.push_back({x - l, x + l});
    }
    int ans = ranges.size() * l - l;
    for (int i = 1; i < ranges.size(); i++) {
        int add = r - l;
        if (i)add = min(add, ranges[i].F - ranges[i - 1].S);
        if (i + 1 != ranges.size())add = min(add, ranges[i + 1].F - ranges[i].S);
        ranges[i].F -= add;
        ranges[i].S += add;
        ans += add;
    }
    if (ans == 0)ans = -1;
    cout << ans << '\n';

}

int32_t main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif // ONLINE_JUDGE

    int t = 1;
//    cin >> t;
    while (t--) {
        doWork();
    }
}