#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n);i++)
#define sz(x) int(x.size())
typedef long long ll;
typedef pair<int,int> P;

int main(){
  int n;
  ll k;
  cin >> n >> k;
  vector<int> a(n), b(n);
  rep(i,n) cin >> a[i] >> b[i];

  auto ok = [&](int x) {
    ll t = 0;
    rep(i,n) {
      if (x >= a[i]) t += min(b[i],x) - a[i] + 1;
    }
    return t >= k;
  };

  int l = 0, r = 1e9;
  while (r - l > 1) {
    int mid = (l + r)/2;
    if (ok(mid)) r = mid;
    else  l = mid;
  }

  cout << r << endl;
  
  return 0;
}