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

template<class T> void vin(vector<T>& v, int n) {
    v.resize(n);
    for (int i = 0; i < n; ++i) {
        cin >> v[i];
    }
}

int main()
{
    ll N, K;
    cin >> N >> K;
    map<ll, ll> mp;
    rep(i, N) {
        ll A, B;
        cin >> A >> B;
        mp[A]++;
        mp[B+1]--;
    }

    ll sum = 0, cur = 0, prev = -1, prevsum = 0;
    for (auto& t : mp) {

        // 間を足す
        if (prev > 0) {
            sum += (t.first - prev - 1) * cur;

            if (sum >= K) {
                ll tmp = K - prevsum;
                ll tmp2 = tmp / cur + bool(tmp%cur);
                cout << prev + tmp2 << endl;
                break;
            }
        }

        // 今の値を足す
        cur += t.second;
        sum += cur;

        if (sum >= K) {
            // Kを超えたとき
            cout << t.first << endl;
            break;
        }
        prev = t.first;
        prevsum = sum;
    }

    return 0;
}