#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<ll> vl;
typedef long double ld;
typedef vector<ld> vd;
typedef bool bl;
typedef vector<bl> vb;
typedef unordered_map<ll,unordered_map<ll,ll>> graph;

const ll e5 = 1 << 20;
const ll mod = 998244353;
const ll e3 = 1 << 13;
const ll INF = 1ll << 60;

ll n,k;
ll a[e5],b[e5];
map<ll,ll> m;
ll dp[e5];
ll ans;

int main(){
  cin >> n >> k;
  for(ll i = 0;i < n;i++) cin >> a[i] >> b[i];
  ll top = 1000000000;
  ll bottom = 0;
  while(top-bottom > 1){
    ll middle = (top+bottom)/2;
    ll mem = 0;
    for(ll i = 0;i < n;i++){
      if(a[i] > middle) continue;
      if(b[i] > middle) mem += middle-a[i]+1;
      else mem += b[i]-a[i]+1;
    }
    if(mem >= k) top = middle;
    else bottom = middle;
  }
  cout << top << endl;

}