#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
const int INF = (int)1e9 + 1001010;
const ll llINF = (long long)4e18 + 22000020;
const string endn = "\n";
template <class T> inline auto vector2(size_t i, size_t j, const T &init = T()) {
    return vector(i, vector<T>(j, init));
}
const string ELM_SEP = " ", VEC_SEP = endn;
template <class T> istream &operator>>(istream &i, vector<T> &A) {
    for(auto &I : A) i >> I;
    return i;
}
template <class T> ostream &operator<<(ostream &o, const vector<T> &A) {
    int sz = A.size();
    for(const auto &I : A) o << I << (--sz ? ELM_SEP : "");
    return o;
}
template <class T> ostream &operator<<(ostream &o, const vector<vector<T>> &A) {
    int sz = A.size();
    for(const auto &I : A) o << I << (--sz ? VEC_SEP : "");
    return o;
}
template <class T> vector<T> &operator++(vector<T> &A, int) {
    for(auto &I : A) I++;
    return A;
}
template <class T> vector<T> &operator--(vector<T> &A, int) {
    for(auto &I : A) I--;
    return A;
}
template <class T, class U> bool chmax(T &a, const U &b) { return ((a < b) ? (a = b, true) : false); }
template <class T, class U> bool chmin(T &a, const U &b) { return ((a > b) ? (a = b, true) : false); }
ll floor_div(ll a, ll b) {
    if(b < 0) a = -a, b = -b;
    return (a >= 0) ? a / b : (a + 1) / b - 1;
}
ll ceil_div(ll a, ll b) {
    if(b < 0) a = -a, b = -b;
    return (a > 0) ? (a - 1) / b + 1 : a / b;
}
bool check_bit(ull val, ull digit) { return (val >> digit) & 1; }
#ifdef DEBUG
#include <cpp-dump/cpp-dump.hpp>
#define dump(...) cpp_dump(__VA_ARGS__)
namespace cp = cpp_dump;
struct InitCppDump {
    InitCppDump() {
        if(!isatty(fileno(stderr))) CPP_DUMP_SET_OPTION(es_style, cpp_dump::types::es_style_t::no_es);
        CPP_DUMP_SET_OPTION(log_label_func, cp::log_label::line());
        CPP_DUMP_SET_OPTION(max_iteration_count, 30);
    }
} init_cpp_dump;
#else
#define dump(...)
#endif
// ==================== ここまでテンプレ ====================


int main(int argc, char *argv[]) {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll n;
    cin >> n;
    vector<ll> x(n), y(n);
    for(int i = 0; i < n; i++) cin >> x[i] >> y[i];
    ll base_score = 0;
    for(int i = 0; i < n; i++) {
        if(x[i] == y[i]) base_score += x[i];
    }

    vector<ll> dp(2, 0);
    for(int i = 1; i < n; i++) {
        vector<ll> ndp(2, -1);
        for(int state = 0; state < 2; state++) {
            for(int nstate = 0; nstate < 2; nstate++) {
                ll val1 = (state == 0) ? y[i - 1] : x[i - 1];
                ll val2 = (nstate == 0) ? x[i] : y[i];
                if(val1 == val2) chmax(ndp[nstate], dp[state] + val1);
                else chmax(ndp[nstate], dp[state]);
            }
        }

        dp = move(ndp);
    }

    ll ans = ranges::max(dp) + base_score;
    cout << ans << endl;
    return 0;
}