#include<bits/stdc++.h>
using namespace std;

int main(){
  using ll=long long;
  ll inf=1e18;
  int n;
  cin>>n;
  vector<vector<ll>> xy(n+1,vector<ll>(2));
  xy[0]={-1,-1};
  for (int i=0;i<n;i++){
    ll x,y;
    cin>>x>>y;
    xy[i+1]={x,y};
  }
  vector<vector<ll>> dp(n+1,vector<ll>(2,-inf));
  dp[0][0]=0;
  for (int i=0;i<n;i++){
    for (int j=0;j<2;j++) for (int k=0;k<2;k++){
      ll val=dp[i][j];
      if (xy[i+1][0]==xy[i+1][1]) val+=xy[i+1][0];
      if (xy[i][j]==xy[i+1][k]) val+=xy[i][j];
      dp[i+1][k^1]=max(dp[i+1][k^1],val);
    }
  }
  ll ans=max(dp[n][0],dp[n][1]);
  cout<<ans<<endl;
}