Polygon area

#include <iostream>

using namespace std;


int main()
{

    long long n;

    cin >> n;
    
    pair<long long, long long> vertices[n];

    for(int i=0; i<n; i++){
        long long a,b;
        cin >> a >> b;
        vertices[i]=make_pair(a,b);
    }

    
    long long area = 0;

    for (long long i = 0; i < n; i++) {
        area += (vertices[i].first * vertices[(i + 1) % n].second - vertices[(i + 1) % n].first * vertices[i].second);
    }

    cout << abs(area) << endl;

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED