There is a hotel with the following accommodation fee:    * X yen (the currency of Japan) per night, for the first K nights   * Y yen per night, for the (K+1)-th and subsequent nights  Tak is staying at this hotel for N consecutive nights. Find his total accommodation fee.
N = int(input())
K = int(input())

X = int(input())
Y = int(input())

print(N*X + (N-K)*Y)
N = int(input())
K = int(input())

X = int(input())
Y = int(input())

print(min(K,N)*X + max(0,(N-K))*Y)
