#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using PII = std::pair<int, int>;
using PLL = std::pair<ll, ll>;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)


vector<vector<int>> donates;

ll coin(int k)
{

    ll a, b, n, l, m, r;
    l = m = r = 0;
    n = donates.size();
    rep(i, n)
    {
        a = donates[i][0], b = donates[i][1];
        if (a <= k && k <= b)
        {
            l += k - a;
            m += 1;
            r += b - k;
        }
        else if (b < k)
            l += b - a + 1;
        else if (a > k)
            r += b - a + 1;
    }

    return l+1;
}

int main()
{

#ifdef DEBUG
    cout << "DEBUG MODE" << endl;
    ifstream in("input.txt"); //for debug
    cin.rdbuf(in.rdbuf());    //for debug
#endif

    int n, k, x;
    ll ok, ng, mid;
    cin >> n >> k;

    donates.resize(n);
    rep(i, n)
    {
        rep(j, 2)
        {
            cin >> x;
            donates[i].push_back(x);
        }
    }
    coin(0);


    ok = 1e9+1, ng = 0;
    while (ok - ng > 1)
    {
        mid = (ok + ng) / 2;

        if (coin(mid) > k)
            ok = mid;
        else
            ng = mid;
    }
    cout << ng << endl;
    return 0;
}