#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<ll,ll> ;
const int INF = 1e9;
const int MOD = 1000000007;
ll n = 100005,k;
vector<P> section(n);

bool ok(ll x){
    ll cnt = 0;
    rep(i,n){
        ll l = section[i].first-1,r = section[i].second+1;
        while(r - l > 1){
            ll m = (l + r)/2;
            if(m < x) l = m;
            else r = m;
        }
        cnt += r - section[i].first ;
    }
    return cnt < k;
}

int main(){
    cin >> n >> k;
    rep(i,n){
        cin >> section[i].first >> section[i].second;
    }
    ll left = -1,right = INF + 1;
    while(right - left > 1){
        ll mid = (left + right)/2;
        if(ok(mid)) left = mid;
        else right = mid;
    }
    cout << left << endl;
    return 0;
}