#include<bits/stdc++.h>

#define ll long long
#define INF 2147483647
#define int long long

int inp(){
    char c = getchar();
    int neg = 1;
    while(c < '0' || c > '9'){
        if(c == '-')
            neg = -1;
        c = getchar();
    }
    int sum = 0;
    while(c >= '0' && c <= '9'){
        sum = sum * 10 + c - '0';
        c = getchar();
    }
    return neg * sum;
}

int pos[100010];
int n, k, a, b;

int solve(int l, int r){
    int cnt = std::upper_bound(pos + 1, pos + k + 1, r) - std::lower_bound(pos + 1, pos + k + 1, l);
    // printf("cnt [%d, %d] = %d\n", l, r, cnt);
    int mid = (l + r) >> 1;
    if(l == r && cnt != 0)
        return (r - l + 1) * cnt * b;
    return (cnt == 0) ? a : std::min((r - l + 1) * cnt * b, solve(l, mid) + solve(mid + 1, r));
}

signed main(){
    n = inp();
    k = inp();
    a = inp();
    b = inp();
    for(int i = 1; i <= k; i++)
        pos[i] = inp();
    std::sort(pos + 1, pos + k + 1);
    printf("%I64d\n", solve(1, 1 << n));
    return 0;
}