#include <bits/stdc++.h>
using namespace std;
using lint = long long;
template<class T = int> using V = vector<T>;
template<class T = int> using VV = V< V<T> >;

int main() {
  cin.tie(nullptr); ios::sync_with_stdio(false);
  int n, k; cin >> n >> k;
  V<> a(n), b(n); for (int i = 0; i < n; ++i) cin >> a[i] >> b[i];
  auto chk = [&](int x) -> bool {
    lint s = 0;
    for (int i = 0; i < n; ++i) {
      s += max(min(b[i], x) - a[i] + 1, 0);
    }
    return s >= k;
  };
  int ng = 0, ok = 1e9;
  while (ok - ng > 1) {
    int mid = ng + ok >> 1;
    (chk(mid) ? ok : ng) = mid;
  }
  cout << ok << '\n';
}