/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.08.13 18:07:30
**/

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

int main() {
    int n;cin >> n;
    vector<int> p(n),a(n);
    for (int i = 0; i < n; i++) {
        cin >> p[i] >> a[i];
    }
    
    vector<vector<ll>> dp(n,vector<ll>(2,0));
    dp[0][0] = a[0];
    dp[0][1] = p[0];
    for (int i = 1; i < n; i++) {
        dp[i][0] = max(dp[i-1][0]+a[i] * 2, dp[i-1][1]+a[i]);
        dp[i][1] = max(dp[i-1][0]+p[i] * 2, dp[i-1][1]+p[i]);
    }
    cout << dp[n-1][1] << endl;
    return 0;
}