#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int n;
int p[100000], a[100000];
long long dp[100000][2];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  cin >> n;
  REP (i, n)
    cin >> p[i] >> a[i];

  dp[n-1][0] = p[n-1];
  dp[n-1][1] = a[n-1];

  for (int i = n - 2; i >= 0; i--) {
    dp[i][0] = p[i] + max(dp[i+1][0], dp[i+1][1]);
    dp[i][1] = a[i] + max(p[i+1] + dp[i+1][0], a[i+1] + dp[i+1][1]);
  }

  cout << max(dp[0][0], dp[0][1]) << endl;
  
  return 0;
}