#include <bits/stdc++.h>
#define rep(i,n) for(int i=(0);i<(n);i++)

using namespace std;

typedef long long ll;

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

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);

	ll n, k;
	cin >> n >> k;

	map<ll, ll> mp;
	rep(i, n){
		ll a, b;
		cin >> a >> b;
		b++;
		if(mp.count(a) == 0) mp[a] = 0;
		mp[a]++;
		if(mp.count(b) == 0) mp[b] = 0;
		mp[b]--;
	}

	ll sm = 0;
	ll t = 0;
	ll x = 0;
	for(auto p : mp){
		ll y = p.first;
		ll z = p.second;
		if(sm + (y - x - 1) * t >= k){
			cout << x + (k - sm + t - 1) / t << endl;
			exit(0);
		}

		sm += (y - x - 1) * t;
		if(sm + (t + z) >= k){
			cout << y << endl;
			exit(0);
		}

		sm += t + z;
		x = y;
		t += z;
	}
}