#include <bits/stdc++.h>
using namespace std;
#define int long long
int32_t main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
pair<int,int> pravoagolnik[n];
for (int i=0;i<n;i++) {
cin >> pravoagolnik[i].first >> pravoagolnik[i].second;
pravoagolnik[i].first/=2;
pravoagolnik[i].second/=2;
}
sort(pravoagolnik, pravoagolnik+n);
int i = 0;
while (i < n - 1 && pravoagolnik[i].first == pravoagolnik[i + 1].first) {
i++;
}
int rez=pravoagolnik[i].first*pravoagolnik[i].second;
int prevWidth = pravoagolnik[i].first;
i++;
for (;i<n;i++) {
if (i < n - 1 && pravoagolnik[i].first == pravoagolnik[i + 1].first) {
continue;
}
rez+=(pravoagolnik[i].first-prevWidth)*pravoagolnik[i].second;
prevWidth = pravoagolnik[i].first;
}
cout << 4*rez << endl;
}
