str = gets.split
x = str[0].to_i
y = str[1].to_i
r = str[2].to_i
s = (x > 0 && y > 0) || (x < 0 && y < 0) ? -1 : 1
u = (y > 0) ? 1 : -1
dist = ->(xx, yy, a, b){ (a * xx - yy + b).abs / Math.sqrt(a ** 2 + 1) }
uu = u
if x != 0 || y != 0 
    while dist[x, y, s, uu] != 0.0 do
        uu += u
    end
end
while dist[x, y, s, uu] - r <= 0.0 do
    uu += u
end
puts uu.abs