#include<iostream>
#include<cstdio>
using namespace std;
int cmp1(int a, int b) {
    return a > b ? a - b : 0;
}
struct bamboo {
    long long a_i, b_i;
};
long long n, left_maxx, right_maxx;
int main() {
    bamboo a[100010];
    cin >> n;
    for(int i = 1; i <= n; i++) {
        cin >> a[i].a_i >> a[i].b_i;
        int c, b;
        c = cmp1(a[i].a_i - a[i].b_i, left_maxx) + cmp1(a[i].b_i, right_maxx);
        b = cmp1(a[i].a_i - a[i].b_i, right_maxx) + cmp1(a[i].b_i, left_maxx);
        if(c > b) left_maxx = max(left_maxx, a[i].a_i - a[i].b_i), right_maxx = max(right_maxx, a[i].b_i);
        else if(c == 0) ;
        else left_maxx = max(left_maxx, a[i].b_i), right_maxx = max(right_maxx, a[i].a_i - a[i].b_i);
    }
    cout << left_maxx + right_maxx;
    return 0;
}

# 4：Wrong Answer.wrong answer On line 1 column 1, read 9, expected 1.