#include<bits/stdc++.h>
#include<atcoder/all>

using namespace std;
using ll = long long;
using P = pair<ll, ll>;

int main() {
    // DP[Nセット目まで見た][前回先置き採用はL:0, R:1] := デカいスコア
    int N; cin >> N;
    vector<P> xy(N);
    for (int i=0;i<N;i++) cin >> xy[i].first >> xy[i].second;
    
    vector DP(N+1, vector<ll>(2, 0));
    for (int i=0;i<N;i++) {
        // l->l
        ll mx_ll =  DP[i][0] + 
            ((xy[i].second == xy[i+1].first) ? xy[i+1].first : 0);
        DP[i+1][0] = max(DP[i+1][0], mx_ll);
        // l->r
        ll mx_lr =  DP[i][0] + 
            ((xy[i].second == xy[i+1].second) ? xy[i+1].second : 0);
        DP[i+1][1] = max(DP[i+1][1], mx_lr);
        // r->l
        ll mx_rl =  DP[i][1] + 
            ((xy[i].first == xy[i+1].first) ? xy[i+1].first : 0);
        DP[i+1][0] = max(DP[i+1][0], mx_rl);
        // r->r
        ll mx_rr =  DP[i][1] + 
            ((xy[i].first == xy[i+1].second) ? xy[i+1].second : 0);
        DP[i+1][1] = max(DP[i+1][1], mx_rr);
    }
    cout << max(DP[N][0], DP[N][1]) << endl;

}