#include <bits/stdc++.h>
using namespace std;
// #include<atcoder/all>
// using mint = atcoder::modint998244353;
using ld = long double;
#define fi first
#define se second
#define all(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(int)(n);++i)
template<typename T>bool chmin(T&a,T b){return b<a?(a=b,1):0;}
template<typename T>bool chmax(T&a,T b){return b>a?(a=b,1):0;}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N;
    cin>>N;
    vector<array<int,2>> A(N);
    rep(i,N)rep(j,2)cin>>A[i][j];

    vector<array<long,2>> dp(N,{(long)-1e18,(long)-1e18});
    dp[0][0]=dp[0][1]=(A[0][0]==A[0][1])*A[0][0];
    for(int i=1;i<N;i++){
        rep(j,2){
            rep(k,2){
                chmax(dp[i][j], dp[i-1][k]+(A[i][j]==A[i-1][1-k])*A[i][j]+(A[i][0]==A[i][1])*A[i][0]);
            }
        }
    }
    cout<<max(dp[N-1][0],dp[N-1][1])<<"\n";

}