from bisect import bisect as bs
def main():
    n, m, a, b = list(map(int, input().split()))
    A = list(map(int, input().split()))
    A.sort()
    X = set()
    for i in range(1, n+1):
        if i*i > n: break
        if not i in A:
            X.add(i)
        if not n//i in A:
            X.add(n//i)
    X = list(X)
    X.sort()
    N = len(X)
    inf = 1<<60
    dp = [inf] * N
    dp[0] = -b
    for i in range(N-1):
        dp[i] += b
        Y = [a for a in A if not a % X[i]]
        for j in range(i+1, N):
            if X[j] % X[i]: continue
            if bs(Y, X[i]) != bs(Y, X[j]): continue
            dp[j] = min(dp[j], dp[i]+(X[j]//X[i]-1)*a)
    #print(dp)
    return dp[-1] if dp[-1] < inf else -1

print(main())