import bisect
import sys
input=sys.stdin.readline

def main(args):
    N, K, bhim, bhmr = map(int,input().split())
    A = list(map(lambda x:-(-(int(x)-1)//K), input().split()))
    A.sort()
    
    prev = 0
    ans = 0
    #print("A :",A)
    for i in range(N):
        #print('##############')
        if A[i] != prev:
            if bhmr < bhim*(N-i):
                ans += bhmr*(A[i]-prev)
            else:
                #残りはベホイミしたほうがいい
                break
            prev = A[i]
            #print(ans)
        A[i] = 0
    
    if sum(A) > 0:
        ans += (sum(A) - (N-i)*prev)*bhim
        
    print(ans)

if __name__ == '__main__':
    main(sys.argv[1:])