#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)


int main(){
    int n; cin >> n;
    vvll x(n, vll(2)); rep(i, n)rep(j, 2)cin >> x[i][j];

    vvll dp(n, vll(2, 0));
    dp[0][0] = dp[0][1] = (x[0][0] == x[0][1]) ? x[0][0] : 0;
    rep2(i, 1, n){
        ll base = (x[i][0] == x[i][1]) ? x[i][0] : 0;
        ll a = dp[i-1][0] , b = dp[i-1][1];
        if(x[i-1][1] == x[i][0]) a += x[i][0];
        if(x[i-1][0] == x[i][0]) b += x[i][0];
        dp[i][0] = max(a, b) + base;
        ll c = dp[i-1][0], d = dp[i-1][1];
        if(x[i-1][1] == x[i][1]) c += x[i][1];
        if(x[i-1][0] == x[i][1]) d += x[i][1];
        dp[i][1] = max(c, d) + base;
    }
    cout << max(dp[n-1][0], dp[n-1][1]) << endl;

    return 0;
}