#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long MOD
= 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;



int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/
	ll N, K; scanf("%lld %lld", &N, &K);
	vector<ll> A(N), B(N);
	for (ll i = 0; i < N; i++) scanf("%lld %lld", &A[i], &B[i]);
	ll l = 0;
	ll r = MOD - 7;
	while (r - l > 1) {
		ll mid = (l + r) >> 1;
		ll cnt = 0;
		for (ll i = 0; i < N; i++) {
			if (A[i] <= mid) {
				ll right = min(mid, B[i]);
				cnt += right - A[i] + 1;
			}
		}
		if (cnt >= K) r = mid;
		else l = mid;
	}
	cout << r << endl;

	return 0;
}