#include "bits/stdc++.h"

using namespace std;

typedef long long LL;

typedef pair<int, int> PII;

const int INF = 0x3f3f3f3f;

const int MAXN = 1e5 + ;

int arr[MAXN];

int n, m, a, b;

// 求摧毁[l, r]这个段最少消耗的能量

LL minPow(int l, int r) {

    int na = lower_bound(arr, arr + m, r + ) - lower_bound(arr, arr + m, l);

    if (na == ) {

        return a;

    }

    LL ans = (r - l + 1LL) * na * b;

    if (r != l) {

        int mid = l + r >> ;

        ans = min(ans, minPow(l, mid) + minPow(mid + , r));

    }

    return ans;

}

int main() {

    scanf("%d%d%d%d", &n, &m, &a, &b);

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

        scanf("%d", &arr[i]);

    }

    sort(arr, arr + m);

    printf("%lld\n", minPow(,  << n));

    return ;

}