#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <string>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <stdio.h>
using namespace std;
#define int long long
int MOD = 1000000007;
signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N, K;
	cin >> N >> K;
	vector<int> A(N);
	vector<int> B(N);
	int res = 0;
	for (int i = 0; i < N; i++) {
		cin >> A[i] >> B[i];
	}

	sort(A.begin(), A.end());
	sort(B.begin(), B.end());
	vector<int> sumA(N + 1, 0);
	vector<int> sumB(N + 1, 0);
	for (int i = 0; i < N; i++) {
		sumA[i + 1] = sumA[i] + A[i];
		sumB[i + 1] = sumB[i] + B[i];
	}

	int ok = 1e9;
	int ng = 0;

	while (ok - ng > 1) {
		int m = (ok + ng) / 2;
		int ans = 0;

		int k = upper_bound(A.begin(), A.end(), m) - A.begin();
		ans += k * m;
		ans -= sumA[k] - k;

		k = upper_bound(B.begin(), B.end(), m) - B.begin();
		ans -= k * m;
		ans += sumB[k];
		//cerr << m << " " << ans << endl;

		if (ans >= K) {
			ok = m;
		}
		else {
			ng = m;
		}
	}


	cout << ok << endl;
}