#include<iostream>
#include<string>
#include<math.h>
#include<algorithm>
#include<vector>
#include<map>
#include<time.h>
#include<set>
#include<stdio.h>
using namespace std;
const long long ma = 10000000;
long long i, n, k, w, v, a[110001] = { 0 }, b[110001] = { 0 }, c[110001] = { 0 }, kr, x, kra[110001] = { 0 };
int main() {

    cin >> n >> k >> w >> v;
    for (i = 0; i < n; i++) {
        kra[i] = -1;
        cin >> a[i];
            if (a[i] >= w)
                b[i] = 1;

        if (v != 0 && b[i] != 0)
            b[i] = min(k,max(b[i], (a[i] - w) / v));
        else if (b[i] != 0)
            b[i] = min(k,i);
        b[i] = min(b[i], max(k, long long(1)));
        if (a[i] >= w)
            b[i] = max(b[i],long long(1));
    }

    kra[0] = n - 1 - b[n - 1];
    kr = kra[0];
    x = 0;
    for (i = n - 2; i >= 0; i--) {
        if (c[i] == 0)
        {
            if (kr <= i)
                c[i] = x + 1;
            else {
                while (kra[x] > i && x < n && kra[x] != -1) {
                    x++;
                }
                kr = kra[x];
                if (x == n) {
                    cout << -1;
                    return 0;
                }
                c[i] = x + 1;
            }
            if (kra[c[i]] == -1 || kra[c[i]]>i - b[i])
                kra[c[i]] = i - b[i];
        }
    }
    cout << c[0] << "\n";
    return 0;
}