inputABCDE = input()
ABCDE = inputABCDE.split()
#print(ABCDE)
A = int(ABCDE[0])
B = int(ABCDE[1])
C = int(ABCDE[2])
D = int(ABCDE[3])
E = int(ABCDE[4])
resultA = A-B#ベーコン０
resultB = A-B+C*(D-E)#ベーコンMAX
if resultA > resultB:
    result = resultA
else:
    result = resultB
print(result)