Polygon area

#include <bits/stdc++.h>

using namespace std;

struct Point {
    long long x, y;
}; 

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int n;
    cin >> n;

    long long area = 0;
    Point ant;
    cin >> ant.x >> ant.y;

    Point first = ant;

    for (int i = 0; i < n-1; ++i) {
        Point act;
        cin >> act.x >> act.y;

        area += ant.x * act.y - act.x * ant.y;
        ant = act;
    }

    area += ant.x * first.y - first.x * ant.y;

    cout << area << endl;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: WRONG ANSWER