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def det(u, v):
    return u[0] * v[1] - u[1] * v[0]
    
def area(xs):
    n = len(xs)
    return abs(sum(det(xs[i], xs[(i + 1) % n]) for i in range(n))) / 2

pts = [(1, 3), (2, 1), (4, 2), (3, -1), (-2, -2), (-3, 2), (-1, 1)]

print(area(pts))
a=lambda xs:abs(sum((lambda u,v:u[0]*v[1]-u[1]*v[0])(xs[i],xs[(i+1)%len(xs)])for i in range(len(xs))))/2
print(a(pts))