#include <iostream>
#include <algorithm>
#include <cstdio>
#define task "COVERING"
using namespace std;
using ll = long long;
using ld = long double;

const int N = 1e5 + 2;

struct Trec{
    ll w, h;
    bool operator < (const Trec& a) const{
        return w < a.w
            ||(w == a.w && h < a.h);
    }
};

Trec a[N];
int n;
ll ans(0);

void Read(){
    cin >> n;
    for(int i = 1; i <= n; ++i){
        cin >> a[i].w >> a[i].h;
        a[i].w /= 2;
        a[i].h /= 2;
    }
    sort(a + 1, a + n + 1);
}

void Solve(){
    ll piv = 1;
    for(int i = n; i; --i){
        if(a[i].h < piv)
            continue;
        ans += (a[i].h - piv + 1) * a[i].w;
        piv = a[i].h + 1;
    }
    cout << ans * 4;
}

main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0); if(fopen(task".INP", "r"))
    freopen(task".INP", "r", stdin),
    freopen(task".OUT", "w", stdout);
    Read();
    Solve();
}