dar, vas, cho = map(int, input().split())
oss = 0
for i in range(0, cho):
    oss = oss + dar
    dar = dar + vas
print(oss)

9eb84aa3620b217cd60098b7e68c031d6ef93ed4
<mask token>

<mask token>
for i in range(0, cho):
    oss = oss + dar
    dar = dar + vas
print(oss)

dar, vas, cho = map(int, input().split())
oss = 0
for i in range(0, cho):
    oss = oss + dar
    dar = dar + vas
print(oss)
