#include "bits/stdc++.h"

using namespace std;

void solve()
{
	int n, k;
	cin >> n >> k;
	vector<long> as(n), bs(n);
	for (int i = 0; i < n; i++)
	{
		cin >> as[i] >> bs[i];
	}
	int ng = 0, ok = 1e9;
	while(ng+1<ok)
	{
		int x = (ok + ng) / 2;
		long res = 0;
		for (int i = 0; i < n; i++)
		{
			if (as[i] > x) continue;
			res += min(bs[i] - as[i], x - as[i]) + 1;
		}
		(res >= k ? ok : ng) = x;
	}
	cout << ok << endl;
}

int main()
{
	solve();
	//cout << "yui(*-v・)yui" << endl;
	return 0;
}