#include <iostream>
#include <algorithm>
using namespace std;
int n, l, r, dp[100009];
int main() {
	cin.tie(0);
	ios_base::sync_with_stdio(false);
	cin >> n;
	for (int i = 0; i <= 100000; i++) dp[i] = -i;
	for (int i = 0; i < n; i++) {
		cin >> l >> r;
		for (int j = r; j >= l; j--) dp[j] = dp[j - 1];
		int val = dp[r] + r;
		for (int j = r + 1; j <= 100000; j++) {
			if (dp[j] + j >= val) break;
			dp[j] = val - j;
		}
	}
	cout << dp[100000] + 100000 << endl;
	return 0;
}