# BUYLAMP - EDITORIALe

Testers: tabr, tejas10p
Editorialist: hrishik85

775

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# PROBLEM:

An electronics shop sells red and blue lamps. A red lamp costs X rupees and a blue lamp costs Y rupees.

Chef is going to buy exactly N lamps from this shop. Find the minimum amount of money Chef needs to pay such that at least K of the lamps bought are red.

# EXPLANATION:

Chef needs at least K lamps red.
The remaining (N-K) lamps can be red or blue.
Also - as per the constraints K \leq N

Hence the minimum amount to pay = (K \times X) + (N - K) \times (min (X,Y))

# TIME COMPLEXITY:

Time complexity is O(1).

# SOLUTION:

Editorialist's Solution
t=int(input())
for _ in range(t):
N,K,X,Y = map(int,input().split())
print(K*X + (N-K)*(min(X,Y)))