#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define mp make_pair
#define pb push_back
#define pf push_front
#define ppb pop_back
#define ppf pop_front
#define speed ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define sz(x) (int)x.size()
#define len(x) (int)strlen(x)
#define all(x) x.begin(), x.end()
#define debug cerr << "OK\n";
#define ub upper_bound
#define lb lower_bound
#define make_unique(x) sort(all(x)), x.erase(unique(all(x)), x.end())
mt19937 bruh(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rofl(chrono::steady_clock::now().time_since_epoch().count());
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef set<int> si;
typedef set<ll> sll;
typedef set<pii> spii;
typedef set<pll> spll;
typedef multiset <int> msi;
typedef multiset <ll> msll;
typedef map <int, int> mi;
typedef map <ll, ll> mll;
const int N = 1e6 + 2;
const int M = 1e5;
const int inf = 2e9 + 3;
const ll INF = 1e18;
const ld pi2 = 2.0 * 3.141592653589793;
const ld pi = 3.141592653589793;
const ld eps = 1e-12;
const int dx[4] = {1, -1, 0, 0};
const int dy[4] = {0, 0, -1, 1};
int n;
int h[10 * N + 200], ans;
int main() {
speed;
cin >> n;
for (int i = 1, x, y; i <= n; ++i) {
cin >> x >> y;
h[x / 2] = max(h[x / 2], y / 2);
}
for (int i = 10 * N; i >= 1; --i) {
h[i] = max(h[i + 1], h[i]);
ans += 4 * h[i];
}
cout << ans << '\n';
}
