#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)(s); i < (int)(e); ++i)

int main() {
	cin.tie(nullptr);
	ios_base::sync_with_stdio(false);
	
	int N;
	cin >> N;
	vector<ll> x(N + 1), y(N + 1);
	rep(i, 1, N + 1) cin >> x[i] >> y[i];
	
	vector dp(N + 1, vector<ll>(2));
	ll sum = 0;
	rep(i, 1, N + 1) {
		if (x[i] == y[i]) sum += x[i];
		
		// x y
		dp[i][0] = max(dp[i - 1][0] + (y[i - 1] == x[i] ? x[i] : 0), dp[i - 1][1] + (x[i - 1] == x[i] ? x[i] : 0));
		
		// y x
		dp[i][1] = max(dp[i - 1][0] + (y[i - 1] == y[i] ? y[i] : 0), dp[i - 1][1] + (x[i - 1] == y[i] ? y[i] : 0));
	}
	cout << max(dp[N][0], dp[N][1]) + sum << '\n';
}