#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define dpmax(a,b) (a = max(a,b))

int main(){
    ll n; cin >> n;
    vector v(n,vector<ll>(2));
    for(ll i = 0;i<n;i++)cin >> v[i][0] >> v[i][1];
    vector dp(n,vector<ll>(2));
    if(v[0][0] == v[0][1])dp[0][0] = dp[0][1] = v[0][0];
    for(ll i = 0;i<n-1;i++){
        ll ex = 0;
        dpmax(dp[i+1][0],max(dp[i][0],dp[i][1]));
        dpmax(dp[i+1][1],max(dp[i][0],dp[i][1]));
        if(v[i+1][0]==v[i+1][1])ex = v[i+1][0];
        for(ll j = 0;j<=1;j++)for(ll k = 0;k<=1;k++){
            if(v[i][j] == v[i+1][k]){
                dpmax(dp[i+1][1-k],dp[i][j] + v[i][j] + ex);
            }
        }
    }
    cout << max(dp[n-1][0],dp[n-1][1]) << endl;
}