#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
#include <set>
#include <unordered_set>
#include <cstring>
#include <queue>
#include <bitset>
#include <map>
#include <stack>

using namespace std;

long long int dp[300005][2];
int n;
long long int x[300005];
long long int y[300005];

int main() 
{
	cin.tie(0);
    ios::sync_with_stdio(false);

	cin >> n;
	for(int i=0;i<n;i++)
	{
		cin >> x[i] >> y[i];
	}

	memset(dp,-1,sizeof(dp));

	if(x[0]==y[0])
	{
		dp[1][0] = x[0];
		dp[1][1] = y[0];
	}
	else 
	{
		dp[1][0] = 0;
		dp[1][1] = 0;
	}

	for(int i=1;i<n;i++)
	{
		long long int score = 0;
		if(x[i]==y[i]) score = x[i];
		if(dp[i][0]!=-1)
		{
			if(x[i-1]==x[i])
			{
				dp[i+1][1] = max(dp[i+1][1],dp[i][0] + score + x[i]);
			}
			else
			{
				dp[i+1][1] = max(dp[i+1][1],dp[i][0] + score);
			}
			if(x[i-1]==y[i])
			{
				dp[i+1][0] = max(dp[i+1][0],dp[i][0] + score + y[i]);
			}
			else
			{
				dp[i+1][0] = max(dp[i+1][0],dp[i][0] + score);
			}			
		}
		if(dp[i][1]!=-1)
		{
			if(y[i-1]==x[i])
			{
				dp[i+1][1] = max(dp[i+1][1],dp[i][1] + score + x[i]);
			}
			else
			{
				dp[i+1][1] = max(dp[i+1][1],dp[i][1] + score);
			}
			if(y[i-1]==y[i])
			{
				dp[i+1][0] = max(dp[i+1][0],dp[i][1] + score + y[i]);
			}
			else
			{
				dp[i+1][0] = max(dp[i+1][0],dp[i][1] + score);
			}	
		}
	}

	cout << max(dp[n][0],dp[n][1]) << '\n';
    return 0;
}