#include <bits/stdc++.h>
using namespace std;
const int maxn = 2 * 1e5 + 10;
int n, a[maxn], b[maxn], max1 = INT_MIN, max2 = INT_MIN;
int main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i] >> b[i];
		max1 = max(max1, b[i]);
		max2 = max(max2, a[i] - b[i]);
	}
	cout << max1 + max2;
	return 0;
}