#include <iostream>
#include <algorithm>
#include <cstring>
#include <sstream>
#include <map>
#include <queue>
#include <vector>
#include <climits>
#define scanf scanf_s
using namespace std;
typedef long long int ll;
typedef pair<ll, ll> pos;
const ll MOD = 1000000007,N=100010;

ll n, k;
pos ab[N];

bool ok(ll v1) {
	ll kv = 0;
	for (int i = 1; i <= n; i++) {
		ll vv1 = ab[i].first, vv2 = ab[i].second;
		kv += max((ll)0, min(v1, vv2) - vv1 + 1);

	}
	return kv >= k;
}

int main() {
	cin >> n >> k;
	for (int i = 1; i <= n; i++)cin >> ab[i].first >> ab[i].second;
	ll mnv = 0, mxv = 1000000010;
	while (mxv - mnv > 1) {
		ll md = (mxv + mnv) / 2;
		if (ok(md))mxv = md;
		else mnv = md;
	}
	cout << mxv << endl;
	return 0;
}