#include <bits/stdc++.h>

#include <atcoder/fenwicktree.hpp>
#include <atcoder/segtree.hpp>
#include <atcoder/modint.hpp>
#include <atcoder/dsu.hpp>
#include <atcoder/lazysegtree.hpp>

using namespace atcoder;
using namespace std;
using ll = long long;
using ull = unsigned long long;
template <class T>
using max_heap = priority_queue<T>;
template <class T>
using min_heap = priority_queue<T, vector<T>, greater<>>;
ll ll_min = numeric_limits<ll>::min();
ll ll_max = numeric_limits<ll>::max();
ll ALPHABET_N = 26;
using mint = modint998244353;
#define rep(i, n) for (ll i = (ll)0; i < (ll)n; i++)
#define rep_(i, k, n) for (ll i = (ll)k; i < (ll)n; i++)
#define all(a) a.begin(), a.end()

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll n;
	cin >> n;
	vector<ll> A(n), B(n);
	rep(i, n) cin >> A[i] >> B[i];
	vector<vector<ll>> dp(n, vector<ll>(2, 0));
	if (A[0] == B[0])
		dp[0][0] = dp[0][1] = A[0];
	rep_(i, 1, n)
	{
		ll x = A[i], y = B[i];
		ll val = (x == y ? x : 0);
		// x パターン
		dp[i][0] = max(dp[i - 1][0] + (x == B[i - 1] ? x : 0), dp[i - 1][1] + (x == A[i - 1] ? x : 0));
		dp[i][0] += val;
		// y パターン
		dp[i][1] = max(dp[i - 1][0] + (y == B[i - 1] ? y : 0), dp[i - 1][1] + (y == A[i - 1] ? y : 0));
		dp[i][1] += val;
	}
	cout << max(dp[n - 1][0], dp[n - 1][1]) << endl;
	return 0;
}