Polygon area

n = int(input())
vertices = []
for i in range(n):
    a, b = map(int, input().split())
    vertices.append((a, b))

res = 0
for v in range(n):
    a1, b1 = vertices[v]
    a2, b2 = vertices[(v + 1) % n]
    res += a1 * b2 - b1 * a2
print(abs(res))

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED