#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int n;
vector<array<int, 2>> v[2];

int main() {
    cin.tie(0)->sync_with_stdio(0);
    cin >> n;
    for(int i=1;i<=n;i++) {
        int a, b; cin >> a >> b;
        v[a <= b].push_back({a, b});
    }
    sort(v[1].begin(), v[1].end());

    ll ans = 0, cur = 0;
    for(auto [x, y] : v[1]) {
        if(cur < x) ans += x-cur, cur = x;
        cur += y-x;
    }

    sort(v[0].begin(), v[0].end(), [&](auto a, auto b){ return make_pair(b[1], a[0]) < make_pair(a[1], b[0]); });
    for(auto [x, y] : v[0]) {
        if(cur < x) ans += x-cur, cur = x;
        cur += y-x;
    }

    cout << ans;
}