import sys
readline = sys.stdin.readline

N, K, X, Y = map(int, readline().split())
A = list(map(int, readline().split()))
A = [-((1-a)//K) for a in A]

if N*X < Y:
    print(X*sum(A))
else:
    s = -(-Y//X)
    A.sort()
    ok = 0
    ng = 10**9+100
    while abs(ok-ng)>1:
        med = (ok+ng)//2
        res = 0
        for a in A:
            if a >= med:
                res += 1
        if res >= s:
            ok = med
        else:
            ng = med
    
    print(Y*ok + X*sum(max(0, a-ok) for a in A ))