Polygon area

def main():
    n = int(input())
    arr = []
    for i in range(n):
        x, y = input().split()
        arr.append((int(x), int(y)))

    res = 0
    for i in range(n - 1):
        res += arr[i][0] * arr[i + 1][1] - arr[i + 1][0] * arr[i][1]
    res += arr[n - 1][0] * arr[0][1] - arr[0][0] * arr[n - 1][1]

    print(res)


if __name__ == "__main__":
    main()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER