#include <bits/stdc++.h>

using namespace std;

using ll = long long;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    ll K;
    cin >> n >> K;
    vector<int> a(n), b(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i] >> b[i];
    }

    ll ng = 0, ok = 1000000000;
    while (ok - ng > 1) {
        ll mid = (ok + ng) / 2;
        ll cnt = 0;
        for (int i = 0; i < n; i++) {
            if (mid < a[i]) continue;
            cnt += min(mid, (ll)b[i]) - a[i] + 1;
        }
        if (cnt >= K) ok = mid;
        else ng = mid;
    }
    cout << ok << endl;
    return 0;
}