#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
const int mod=1000000007;

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n,k;cin >> n >> k;
	vector<int> a(n),b(n);
	rep(i,n) cin >> a.at(i) >> b.at(i);
	int l=1,r=1000000000;
	while(r-l>1){
		int mid=(r+l)/2;
		ll cnt=0;
		rep(i,n){
			if(a.at(i)<=mid && mid<=b.at(i)){
				cnt+=mid-a.at(i)+1;
			}
			else if(b.at(i)<mid){
				cnt+=b.at(i)-a.at(i)+1;
			}
		}
		if(cnt>=k) r=mid;
		else l=mid;
	}
	cout << r << endl;
}