#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

inline ll f(ll a, ll b) {
  return a == b ? a : 0;
}

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int n;
  cin >> n;
  vector<pair<int, int>> v(n);
  rep(i, n) cin >> v[i].first >> v[i].second;
  vector dp(n + 1, vector<ll>(2, -1e18));
  dp[1][0] = dp[1][1] = f(v[0].first, v[0].second);
  for (int i = 1; i < n; ++i) {
    ll val = f(v[i].first, v[i].second);
    dp[i + 1][0] = max(dp[i][0] + f(v[i - 1].second, v[i].first) + val, dp[i][1] + f(v[i - 1].first, v[i].first));
    dp[i + 1][1] = max(dp[i][0] + f(v[i - 1].second, v[i].second) + val, dp[i][1] + f(v[i - 1].first, v[i].second));
  }
  cout << max(dp[n][0], dp[n][1]) << '\n';
  return 0;
}