#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    int n;ll k;cin>>n>>k;
    vector<pair<ll,ll>> v(n);
    rep(i,n){
        cin>>v[i].first>>v[i].second;
    }
    
    auto check=[&](ll m){
        ll cnt=0;
        rep(i,n){
            cnt+=max(0ll,min(m,v[i].second)-v[i].first+1);
        }
        return cnt>=k;
    };

    ll lw=0,hi=10ll*INF,res;
    while(lw<=hi){
        ll mid=(lw+hi)/2;
        if(check(mid)){
            res=mid;
            hi=mid-1;
        }else{
            lw=mid+1;
        }
    }
    cout<<res<<endl;
    return 0;
}