#include<iostream>
#include<atcoder/all>
#include<vector>
#include<algorithm>
#include<bits/stdc++.h>
#include<math.h>
#include <numeric>
#include <random>
#include<map>
#include<queue>
#include<deque>
#include <bitset>
#include<stack>
#include<set>
using namespace std;
using namespace atcoder;
#define int long long
using mint=modint998244353;
double pi=3.141592653589793128;
//cout << fixed << setprecision(10);
#define all(x) (x).begin(),(x).end()
#define rep(i,n) for (int i=0;i<(n);++i)
#define prep(i,n) for (int i=1;i<=(n);++i)
#define ep(i,j,n) for (int i=j+1;i<=(n);++i)
long long INF = 900000000000000;
int mod=998244353;

signed main(){
   int n;cin>>n;
   int dp[n][2];
   rep(i,n){
   	rep(j,2)dp[i][j]=0;
   }
   int x[n],y[n];int ans=0;
   rep(i,n)cin>>x[i]>>y[i];
   if(x[0]==y[0]){dp[0][0]=x[0];dp[0][1]=x[0];}
   prep(i,n-1){
   	if(x[i]==x[i-1])dp[i][0]=dp[i-1][1]+x[i];
   	if(y[i]==y[i-1])dp[i][1]=dp[i-1][0]+y[i];
   	if(x[i]==y[i-1])dp[i][0]=dp[i-1][0]+x[i];
   	if(y[i]==x[i-1])dp[i][1]=dp[i-1][1]+y[i];
   	rep(j,2){
   		rep(k,2){
   			dp[i][k]=max(dp[i][k],dp[i-1][j]);
   		}
   	}
   	if(x[i]==y[i]){
   		rep(j,2)dp[i][j]+=x[i];
   	}
   }
   cout<<max(dp[n-1][0],dp[n-1][1]);
}