from math import floor, ceil, sqrt
from decimal import Decimal

x, y, r = map(Decimal, input().split())

ans = 0
for i in range(ceil(x-r), floor(x+r)+1):
    y2 = r**2 - (Decimal(i)-x)**2
    if y2<0: continue
    tp = floor((y2.sqrt() + y))
    bt = ceil((-y2.sqrt() + y))
    ans += tp - bt + 1
print(ans)
