#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
using Data = pair<ll, vector<int>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };

vector <pair <ll ,ll>> dat;
ll n, k;

int check(ll m) {
	ll temp = 0;
	fore(x, dat) {
		if (x.first > m)continue;
		else if (x.second < m)temp += (x.second - x.first)+1;
		else if (x.first <= m && m <= x.second)temp += (m - x.first) + 1;
	}
	return temp >= k;
}

int main() {
	cin >> n >> k;

	rep(i, 0, n) {
		ll a, b;
		cin >> a >> b;
		dat.pb({ a,b });
	}

	
	ll ng = 0; ll ok = 1000000001;
	while (ok - ng > 1) {
		ll mid = (ng + ok) / 2;
		if (check(mid))ok = mid;
		else ng = mid;
	}
	cout << ok << endl;



	return 0;
}