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

// コンテスト中のみ
//#define int long long

#define ll long long
#define rep(i,n) for(int i = 0; i < (n); i++)
#define P pair<ll,ll>
#define ld long double
ll INF = (1LL << 60);
int MOD = 1000000007;
ll N;
ll p[100010], a[100010];
ll dp[100010][2];
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cin >> N;
	rep(i, N)cin >> p[i] >> a[i];
	dp[0][0] = p[0], dp[0][1] = a[0];
	for (int i = 1; i < N; i++) {
		dp[i][0] = max(dp[i - 1][0] + p[i], dp[i - 1][1] + p[i] * 2);
		dp[i][1] = max(dp[i - 1][0] + a[i], dp[i - 1][1] + a[i] * 2);
	}
	ll ans = 0;
	rep(i, 2)ans = max(ans, dp[N - 1][i]);
	cout << ans << endl;
	return 0;
}