def f(x):
    return()
a = float(input())
b = float(input())
eps = float(input())
while abs(b - a) > eps:
        x = (a + b) / 2.0
        fx = f(x)
        fa = f(a)
        if (fx < 0 and fa < 0) or (fx > 0 and fa > 0):
            a = x
        else:
            b = x
print(x)