T = int(input())
ans = 0
L = 0
R = 0
A = 0
B = 0

for i in T:
    L,R,A,B = map(int,input().split())
    if A > 0:
        ans = A * R + B
    elif A < 0:
        ans = A * L + B
    else:
        ans = B
print(ans)