w,h,k=map(int,input().split())
s=0
for i in range(k,0,-1):
s+=2*(w-4*(i-1))+2*(h-4*(i-1))-4
print(s)1204B - Mislove Has Lost an Array | 1409D - Decrease the Sum of Digits |
1476E - Pattern Matching | 1107A - Digits Sequence Dividing |
1348A - Phoenix and Balance | 1343B - Balanced Array |
1186A - Vus the Cossack and a Contest | 1494A - ABC String |
1606A - AB Balance | 1658C - Shinju and the Lost Permutation |
1547C - Pair Programming | 550A - Two Substrings |
797B - Odd sum | 1093A - Dice Rolling |
1360B - Honest Coach | 1399C - Boats Competition |
1609C - Complex Market Analysis | 1657E - Star MST |
1143B - Nirvana | 1285A - Mezo Playing Zoma |
919B - Perfect Number | 894A - QAQ |
1551A - Polycarp and Coins | 313A - Ilya and Bank Account |
1469A - Regular Bracket Sequence | 919C - Seat Arrangements |
1634A - Reverse and Concatenate | 1619C - Wrong Addition |
1437A - Marketing Scheme | 1473B - String LCM |