Polygon area

#include <cstdlib>
#include <iostream>
#include <utility>
#include <vector>


typedef long long l;

int main(){
  int n;
  std::cin >> n;
  std::vector<std::pair<l, l>> points(n + 1);
  for (int i = 0; i<n; ++i){
    l x, y;
    std::cin >> x >> y;
    points[i] = {x, y};
  }
  points[n] = points[0];

  l area = 0;
  for (int i = 0; i<n; ++i){
    area += points[i].first * points[i+1].second - points[i+1].first * points[i].second;
  }

  area = std::abs(area);

  std::cout << area << "\n";
  
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED