// includes
#include <bits/stdc++.h>

// macros
#define ll long long int
#define pb emplace_back
#define mk make_pair
#define pq priority_queue
#define FOR(i, a, b) for(int i=(a);i<(b);++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for(int i=((int)(n)-1);i>=0;i--)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)(x).size())
#define UNIQUE(v) v.erase(unique(v.begin(), v.end()), v.end())
#define FI first
#define SE second
using namespace std;

//  types
typedef pair<int, int> P;
typedef pair<ll, int> Pl;
typedef pair<ll, ll> Pll;
typedef pair<double, double> Pd;
 
// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double EPS = 1e-10;
const int mod = 1e9 + 7;

// solve
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;}
template <typename T> istream &operator>>(istream &is, vector<T> &vec){for(auto &v: vec)is >> v; return is;}


ll A[100001], B[100001];

int main(int argc, char const* argv[])
{
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  rep(i, n){
    cin >> A[i] >> B[i];
    //cerr << A[i] << " " << B[i] << endl;
  }

  ll l = 1, r = 1e9 + 1;
  while(r - l > 1){
    ll m = (l + r) / 2;
    ll tmp = 0;
    for(int i = 0; i < n; i++){
      if(B[i] <= m)tmp += B[i] - A[i] + 1;
      else if(A[i] <= m && m <= B[i])tmp += m - A[i] + 1;
    }
    //cout << m << " " << tmp << endl;
    if(tmp >= k)r = m;
    else l = m;
  }
  cout << l + 1 << endl;
	return 0;
}