x,y,r=map(int,input().split())
x,y=abs(x),abs(y)
if x>y: x,y=y,x # always x<y

for i in range(200):
    if i>x*2+r*(2**0.5):
#    if i/(2**0.5)>x*(2**0.5)+r:
        print(i+y-x)
        break