#include<bits/stdc++.h>

int main() {
	using namespace std;
	cin.tie(nullptr)->sync_with_stdio(false);
	int N; cin >> N;

	using i64 = int64_t;

	vector<i64> S(N), E(N);
	for (int i = 0; i < N; ++i) cin >> S[i] >> E[i];

	vector<int> id(N); iota(id.begin(), id.end(), 0);

	sort(id.begin(), id.end(), [&](const auto& i, const auto& j) {
		i64 lhs = E[i] - S[i];
		i64 rhs = E[j] - S[j];
		if (lhs >= 0 && rhs < 0) return true;
		if (lhs < 0 && rhs >= 0) return false;
		if (lhs < 0 && rhs < 0) return E[i] < E[j];
		return S[i] < S[j];
	});

	i64 cur = 0, ans = 0;
	for (int i = 0; i < N; ++i) {
		if (S[id[i]] > cur) {
			ans += S[id[i]] - cur;
			cur = S[id[i]];
		}
		cur += E[id[i]] - S[id[i]];
	}

	cout << ans << '\n';
}