#include <algorithm>
#include <cassert>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iostream>
#include <numeric>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <functional>
#include <iomanip>
#include <ranges>
using namespace std;
using ll = long long;

template<typename T> auto range(T s, T e) { return views::iota(s, max(s, e)); }
template<typename T> auto range(T n) { return range<T>(0, n); }
template<typename T> void take(vector<T>& vec, int n) { vec.resize(n); for (int i = 0; i < n; ++i) cin >> vec[i]; }
template<class... Args> void sout(const Args &...args) { ((cout << args << ' '), ...); }
template<class... Args> void soutn(const Args &...args) { ((cout << args << ' '), ...); cout << '\n'; }
template<typename T1, typename T2> struct In2 {
  T1 a; T2 b; friend std::istream& operator>>(std::istream& is, In2& obj) { T1 t1; T2 t2; is >> t1 >> t2; obj = {t1, t2}; return is; } };
template<typename T1, typename T2, typename T3> struct In3 {
  T1 a; T2 b; T3 c; friend std::istream& operator>>(std::istream& is, In3& obj) { T1 t1; T2 t2; T3 t3; is >> t1 >> t2 >> t3; obj = {t1, t2, t3}; return is; } };
template<typename T1, typename T2, typename T3, typename T4> struct In4 {
  T1 a; T2 b; T3 c; T4 d; friend std::istream& operator>>(std::istream& is, In4& obj) { T1 t1; T2 t2; T3 t3; T4 t4; is >> t1 >> t2 >> t3 >> t4; obj = {t1, t2, t3, t4}; return is; } };

#ifdef LOCAL
#include <debug.h>
#else
#define dump(...) ;
#endif


namespace {

ll n; vector<In2<ll, ll>> va;

void read() {
  cin >> n; take(va, n);
}


ll run() {
  vector<ll> dpx(n + 1), dpy(n + 1);
  for (int i : range(n)) {
    auto [xi, yi] = va[i];
    ll xp = -1, yp = -1;
    if (i) {
      xp = va[i - 1].a;
      yp = va[i - 1].b;
    }

    dpx[i + 1] = max(
        dpx[i] + (xp == yi ? yi : 0LL),
        dpy[i] + (yp == yi ? yi : 0LL)
    );
    dpy[i + 1] = max(
        dpx[i] + (xp == xi ? xi : 0LL),
        dpy[i] + (yp == xi ? xi : 0LL)
    );
  }
  ll s = 0;
  for (auto [x, y] : va) if (x == y) s += x;

  return max(dpx[n], dpy[n]) + s;
}

}  // namespace

template <typename F>
void exec(F f) { if constexpr (std::is_same_v<decltype(f()), void>) f(); else cout << f() << endl; }

int main(int argc, char** argv) {
  cerr << fixed << setprecision(12);
  cout << fixed << setprecision(12);
  int testcase = 1;
  if (argc > 1) testcase = atoi(argv[1]);
  while (testcase--) {
    read();
  }
  exec(run);
}