#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <algorithm>
#include <iomanip>
#include <numeric>
using namespace std;
using ll = long long;
int main() {
	int N;cin >> N;
	vector<ll> X(N), Y(N);
	for (int i = 0;i < N;i++) cin >> X[i] >> Y[i];
	vector<ll> dp(2, 0);
	if (X[0] == Y[0]) {
		dp[0] = X[0];
		dp[1] = X[0];
	} 
	for (int i = 0;i < N-1;i++) {
		vector<ll> ndp(2, 0);
		for (int t = 0;t < 2;t++) for (int u = 0;u < 2;u++) {
			ll np = Y[i];
			if (t == 1) np = X[i];
			ll nx = X[i+1];
			if (u == 1) nx = Y[i+1];
			ndp[u] = max(ndp[u], (X[i+1]==Y[i+1] ? X[i+1] : 0) + (nx == np ? nx : 0) + dp[t]);
		}
		swap(dp, ndp);
	}
	cout << max(dp[0], dp[1]) << endl;
}