#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

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

  int n, k;
  cin >> n >> k;
  vector<int> a(n), b(n);
  REP (i, n) cin >> a[i] >> b[i];

  int hi = 1e9;
  int lo = 0;
  
  while (hi - lo > 1) {
    int mi = (lo + hi) / 2;
    long long cnt = 0;

    REP (i, n) {
      if (mi >= b[i]) cnt += b[i] - a[i] + 1;
      else if (mi >= a[i]) cnt += mi - a[i] + 1;
    }

    if (cnt >= k)
      hi = mi;
    else
      lo = mi;
  }
  cout << hi << endl;
  
  return 0;
}