#include <iostream>
#include <vector>

using lint = long long;

void solve() {
    int n;
    lint k;
    std::cin >> n >> k;

    std::vector<std::pair<lint, lint>> ps(n);
    for (auto& p : ps) std::cin >> p.first >> p.second;

    lint ok = 0, ng = 1 << 30;
    // the number of coins less than ok is smaller than k
    while (ng - ok > 1) {
        lint mid = (ok + ng) / 2;

        lint sum = 0;
        for (auto p : ps) {
            if (mid <= p.first) continue;

            lint r = std::min(mid - 1, p.second);
            sum += r - p.first + 1;
        }

        if (sum < k) {
            ok = mid;
        } else {
            ng = mid;
        }
    }

    std::cout << ok << "\n";
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}