#include <bits/stdc++.h>
using namespace std;
#define ALL(x) (x).begin(), (x).end()
#define REP(i, n) for(int i=0; i<n; i++)
bool chmax(auto& a, auto b) { return a<b ? a=b, true : false; }
bool chmin(auto& a, auto b) { return a>b ? a=b, true : false; }
using ll=long long; const int INF=1e9+10; const ll INFL=4e18;

#ifdef DEBUG
#include "./debug.hpp"
#else
#define debug(...)
#define print_line
#endif

//----------------------------------------------------------

void solve() {
    ll N; cin>>N;
    vector<ll> X(N),Y(N); REP(i,N) cin>>X[i]>>Y[i];

    vector<map<ll,ll>> dp(N+1);
    dp[0][-1]=0;
    REP(i,N) {
        for(auto [back,val]: dp[i]) {
            //xy
            {
                ll nval=val;
                if(back==X[i]) nval+=back;
                if(X[i]==Y[i]) nval+=X[i];
                chmax(dp[i+1][Y[i]],nval);
            }
            {
                swap(X[i],Y[i]);
                ll nval=val;
                if(back==X[i]) nval+=back;
                if(X[i]==Y[i]) nval+=X[i];
                chmax(dp[i+1][Y[i]],nval);
                swap(X[i],Y[i]);
            }
        }
    }

    ll ans=0;
    for(auto [x,y]: dp.back()) chmax(ans,y);
    cout<<ans<<endl;
}

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    //cout<<fixed<<setprecision(15);
    int T=1; //cin>>T;
    while(T--) solve();
}