#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;

int main(){
  ll N, K;
  cin >> N >> K;
  vector<vector<ll>> v;
  rep(i,N){
    ll A, B;
    cin >> A >> B;
    v.push_back({A,B});
  }

  ll lb = 0, ub = 1000000005;
  while(ub-lb>1){
    ll m = (lb + ub)/2;

    ll cnt = 0;
    rep(i,N){
      if(v[i][1] <= m) cnt += v[i][1] - v[i][0] + 1;
      else if(v[i][0] <= m && m < v[i][1]) cnt += m - v[i][0] + 1;
    }
    if(cnt<=K) lb = m;
    else ub = m;
  }

  cout << ub << endl;
  
  return 0;
}