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

int N;

signed main(){
  cin>>N;
  vector<vector<int>> dp(N+1,vector<int>(2));
  vector<int> X(N+1,-1);
  vector<int> Y(N+1,-1);
  for(int i = 1; i <= N; i++){
  	cin>>X[i]>>Y[i];
  	if(X[i] == Y[i]) dp[i-1][0] += X[i];
  	if(X[i] == Y[i]) dp[i-1][1] += X[i];
  	dp[i][0] = dp[i][1] = max(dp[i-1][0],dp[i-1][1]);
  	if(X[i] == X[i-1]) dp[i][0] = max(dp[i][1],dp[i-1][1] + X[i]);
  	if(X[i] == Y[i-1]) dp[i][0] = max(dp[i][1],dp[i-1][0] + X[i]);
  	if(Y[i] == X[i-1]) dp[i][1] = max(dp[i][0],dp[i-1][1] + Y[i]);
  	if(Y[i] == Y[i-1]) dp[i][1] = max(dp[i][0],dp[i-1][0] + Y[i]);
  }
  cout << max(dp[N][0],dp[N][1]) << "\n";
}