#include <bits/stdc++.h>
using namespace std;

int main()
{
	int64_t n, k;
	cin >> n >> k;
	vector<pair<int64_t, int64_t>> ps(n);
	for (auto &p : ps)
	{
		cin >> p.first >> p.second;
	}
	auto f = [](vector<pair<int64_t, int64_t>> &ps, int64_t x) {
		int64_t r = 0;
		for (auto &p : ps)
		{
			if (p.first <= x)
			{
				r += min(x, p.second) - p.first + 1;
			}
		}
		return r;
	};
	int64_t l = 0, r = (1LL << 60);
	while (1 < r - l)
	{
		int64_t mid = (l + r) / 2;
		((f(ps, mid) < k) ? l : r) = mid;
	}
	cout << r << endl;
	return 0;
}