#include <bits/stdc++.h>
#define ll long long
using namespace std;
ll n, maxx1 = -1, maxx2 = -1, s1, d1, i;

struct lin {
	int a, b;
} arr[100010];

int main() {
	cin >> n;
	for (i = 1; i <= n; i++) {
		cin >> arr[i].a >> arr[i].b;
		ll line1 = arr[i].a - arr[i].b, line2 = arr[i].b;
		if (maxx1 < line1) {
			s1 = i, d1 = 1;
			maxx1 = line1;
		}
		if (maxx1 < line2) {
			s1 = i, d1 = 2;
			maxx1 = line2;
		}
	}
	for (i = 1; i <= n; i++) {
		ll line1 = arr[i].a - arr[i].b, line2 = arr[i].b;
		if (maxx2 < line1) {
			if (s1 == i && d1 == 1)
				continue;
			maxx2 = line1;
		}
		if (maxx2 < line2) {
			if (s1 == i && d1 == 2)
				continue;
			maxx2 = line2;
		}
	}
	cout << maxx1 + maxx2 << endl;
	return 0;
}