#include <cstdio>

#include <algorithm>

#define lson ls[x]

#define rson rs[x]

#define N 10000006

#define ll long long

#define setIO(s) freopen(s".in","r",stdin)

using namespace std;

ll A,B;

int n,k,tot;

int ls[N],rs[N],sum[N];

void update(int &x,int l,int r,int p)

{

    if(!x) x=++tot;

    ++sum[x];

    if(l==r) return;

    int mid=(l+r)>>1;

    if(p<=mid)  update(lson,l,mid,p);

    else update(rson,mid+1,r,p);

}

ll query(int x,int l,int r)

{

    if(!x) return A;

    if(l==r) return B*sum[x];

    int mid=(l+r)>>1;

    ll re=B*1ll*(r-l+1)*sum[x];

    return min(re,query(lson,l,mid)+query(rson,mid+1,r));

}

int main()

{

    // setIO("input");

    int i,j,bs=1,rt=0;

    scanf("%d%d%lld%lld",&n,&k,&A,&B);

    for(i=1;i<=n;++i)  bs<<=1;

    for(i=1;i<=k;++i)

    {

        int po;

        scanf("%d",&po),update(rt,1,bs,po);

    }

    printf("%lld\n",query(rt,1,bs));

    return 0;

}