/* -*- coding: utf-8 -*-
 *
 * 1160.cc:  No.1160 Strange Bowling - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

/* global variables */

int ps[MAX_N], as[MAX_N];
int dp[MAX_N + 1][2];

/* subroutines */

inline void setmax(int &a, int b) { if (a < b) a = b; }

/* main */

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d%d", ps + i, as + i);

  dp[0][0] = 0, dp[0][1] = -1;
  for (int i = 0; i < n; i++) {
    if (dp[i][0] >= 0) {
      setmax(dp[i + 1][0], dp[i][0] + ps[i]);
      setmax(dp[i + 1][1], dp[i][0] + as[i]);
    }
    if (dp[i][1] >= 0) {
      setmax(dp[i + 1][0], dp[i][1] + ps[i] * 2);
      setmax(dp[i + 1][1], dp[i][1] + as[i] * 2);
    }
  }

  printf("%d\n", dp[n][0]);
  return 0;
}