#include<bits/stdc++.h>

#define LL long long

#define fi first

#define se second

#define mk make_pair

#define PLL pair<LL, LL>

#define PLI pair<LL, int>

#define PII pair<int, int>

#define SZ(x) ((int)x.size())

#define ull unsigned long long

using namespace std;

const int N = 2e5 + ;

const int inf = 0x3f3f3f3f;

const LL INF = 0x3f3f3f3f3f3f3f3f;

const int mod = 1e9 + ;

const double eps = 1e-;

const double PI = acos(-);

int n, k, b, c, t[N];

PII a[N];

LL ans = INF;

LL cnt = ;

priority_queue<PLI> que;

LL solve(PII *a, LL b, LL c) {

    while(!que.empty()) que.pop();

    cnt = ;

    LL ans = INF, ret = ;

    for(int i = ; i <= k; i++) {

        ret += a[i].se * c;

        ret += (a[i].fi - a[i - ].fi) * cnt * b;

        que.push(mk(c * a[i].se + (a[].fi - a[i].fi) * b, i));

        cnt++;

    }

    ans = min(ans, ret);

    for(int i = k + ; i <= n; i++) {

        int p = que.top().se; que.pop(); cnt--;

        ret -= a[p].se * c;

        ret -= (a[i - ].fi - a[p].fi) * b;

        ret += (a[i].fi - a[i - ].fi) * cnt * b;

        ret += a[i].se * c;

        que.push(mk(c * a[i].se + (a[].fi - a[i].fi) * b, i));

        cnt++;

        ans = min(ans, ret);

    }

    return ans;

}

int main() {

    scanf("%d%d%d%d", &n, &k, &b, &c);

    for(int i = ; i <= n; i++) scanf("%d", &t[i]), t[i] += ;

    sort(t + , t +  + n);

    for(int i = ; i <= n; i++) a[i].fi = t[i], a[i].se = ;

    ans = min(ans, solve(a, c, ));

    for(int j = ; j < ; j++) {

        for(int i = ; i <= n; i++) {

            a[i].se = ((j - (t[i] % )) + ) % ;

            a[i].fi = (t[i] + a[i].se) / ;

        }

        ans = min(ans, solve(a, b, c));

    }

    printf("%lld\n", ans);

    return ;

}

/*

*/