def area_trapezi(p1, p2):
    l = p2.x -p1.x
    h = p2.y -p1.y
    return p1.y*l + 0.5*h*l

def area(pol):
    area = 0
    for aresta in pol.iter_arestes():
        area = area + area_trapezi(aresta[0], aresta[1])
    return abs(area)