/*
* 特别处理有一个杆子超级长？
 */

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int n;
    std::cin >> n;

    std::vector<int> half_lengths;
    half_lengths.reserve(2 * n);
    for (int i = 0; i < n; i++) {
        int length, flag_pos;
        std::cin >> length >> flag_pos;
        half_lengths.push_back(length - flag_pos);
        half_lengths.push_back(flag_pos);
    }
    std::sort(half_lengths.begin(), half_lengths.end(), std::greater<>());

    std::cout << half_lengths[0] + half_lengths[1] << std::endl;

    return 0;
}