1

#include <bits/stdc++.h>
#ifndef HOME
    #pragma GCC optimize("unroll-loops")
    #pragma GCC target("avx")
    #pragma GCC optimize("Ofast")
#endif
using namespace std;
long long n,k,a,b;
long long v[100001];
long long cautbin(long long poz)
{
    int r=0,pas=1<<16;
    while(pas)
    {
        if(r+pas<=k&&v[r+pas]<=poz)
            r+=pas;
        pas>>=1;
    }
    return r;
}
long long destroy(long long st,long long dr)
{
    long long x=cautbin(st-1),y=cautbin(dr);
    long long na=y-x;
    if(na==0)
        return a;
    return na*1LL*b*1LL*(dr-st+1);
}
long long rez(long long st,long long dr)
{
    if(destroy(st,dr)==a)
        return a;
    if(st==dr)
        return destroy(st,dr);
    return min(rez(st,(st+dr)/2)+rez((st+dr)/2+1,dr),destroy(st,dr));
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
#ifdef HOME
    freopen("test.in","r",stdin);
    freopen("test.out","w",stdout);
#endif
    cin>>n>>k>>a>>b;
    for(long long i=1; i<=k; i++)
        cin>>v[i];
    sort(v+1,v+k+1);
    cout<<rez(1,(1LL<<n));
    return 0;
}