#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;

#define rep(i,n) for(ll i=0;i<n;++i)
#define all(a) (a).begin(),(a).end()
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
template<class T> T div_floor(T a, T b) { return a / b - ((a ^ b) < 0 && a % b); }
template<class T> T div_ceil(T a, T b) { return a / b + ((a ^ b) > 0 && a % b); }
template <typename T, typename U> inline bool chmin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template <typename T, typename U> inline bool chmax(T &x, U y) { return (x < y) ? (x = y, true) : false; }

template<typename T>
ostream &operator<<(ostream &os, const vector<T> &a){
    if (a.empty()) return os;
    os << a.front();
    for (auto e : a | views::drop(1)){
        os << ' ' << e;
    }
    return os;
}

void dump(auto ...vs){
    ((cout << vs << ' '), ...) << endl;
}



void solve() {
    ll N;
    cin>>N;
    ll bx,by;
    bx=-1;
    by=-1;
    vector<ll> dp(2,0);
    rep(i,N){
        ll x,y;
        cin>>x>>y;
        vector<ll> ndp(2,0);
        chmax(ndp[0],dp[0]+((by==x)*x));
        chmax(ndp[0],dp[1]+((bx==x)*x));
        chmax(ndp[1],dp[0]+((by==y)*y));
        chmax(ndp[1],dp[1]+((bx==y)*y));
        if (x==y){
            ndp[0]+=x;
            ndp[1]+=x;
        }
        swap(x,bx);
        swap(y,by);
        swap(dp,ndp);
    }
    cout<<*max_element(all(dp))<<endl;
    return;
}


int main() {
    cin.tie(0)->sync_with_stdio(0);
    ll T=1;
    while (T--){
        solve();
    }
    return 0;
}