from math import exp, sin

a,b,eps=map(float,input('\n').split())

def f(x):
        return sin(x)

def rectangle(f,a,b,eps):
        steps = 1/eps
        dx, area, x = (b-a)/steps, 0, a
        for i in range(int(steps)):
            area+= abs(f(dx*i))
        return area*dx

def rectangleEPS(f,a,b,eps):
        eps1 = eps*2;
        area = rectangle(f,a,b,eps1)
        while abs(rectangle(f,a,b,eps) - rectangle(f,a,b,eps1)) > eps:
            area = rectangle(f,a,b,eps1)
            eps1*=2
        return area

print('', rectangleEPS(f,a,b,eps))

input()