#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N;
	cin >> N;
	int dp[2] {};
	dp[1] = -INF;
	REP(i, N) {
		int p, a;
		scanf("%d %d", &p, &a);
		
		int ndp[2];
		ndp[0] = max(dp[0] + p, dp[1] + 2 * p);
		ndp[1] = max(dp[0] + a, dp[1] + 2 * a);
		memcpy(dp, ndp, sizeof(dp));
	}
	cout << max(dp[0], dp[1]) << endl;
}