#include <bits/stdc++.h>
#define pt(sth) cout << sth << "\n"
#define chmax(a, b) {if(a<b) a=b;}
#define chmin(a, b) {if(a>b) a=b;}
#define moC(a, s, b) (a)=((a)s(b)+MOD)%MOD
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
static const ll INF=1e18;
static const ll MAX=101010;
static const ll MOD=1e9+7;


ll N, K;
ll a[MAX], b[MAX];

ll C(ll x) {
  ll cnt=0;
  for(ll i=0; i<N; i++) {
    if(a[i]<=x) {
      cnt+=min(x-a[i], b[i]-a[i]);
    }
  }
  return cnt>=K;
}

int main(void) {
  cin >> N >> K;
  ll i;
  
  for(i=0; i<N; i++) {
    cin >> a[i] >> b[i];
    b[i]++;
  }
  
  ll l=0, r=INF;
  while(l+1<r) {
    ll mid=(l+r)/2;
    if(C(mid)) r=mid;
    else l=mid;
  }
  
  pt(l);
}