mod = 1000000007
eps = 10**-9


def main():
    import sys
    input = sys.stdin.readline

    N, K, X, Y = map(int, input().split())
    A = list(map(int, input().split()))

    B = [0] * N
    for i in range(N):
        if A[i] == 1:
            continue
        B[i] = (A[i] - 2) // K + 1
    B.sort(reverse=True)
    ans = B[0] * Y
    cnt = 0
    for i in range(1, N):
        cnt += (B[i-1] - B[i]) * X * i
        ans = min(ans, cnt + Y * B[i])
    ans = min(ans, X * sum(B))
    print(ans)


if __name__ == '__main__':
    main()