#include <iostream>
#include <vector>

using lint = long long;

int main() {
    lint N, K;
    std::cin >> N >> K;

    std::vector<int> A(N), B(N);
    for (int i = 0; i < N; ++i) {
        std::cin >> A[i] >> B[i];
    }

    int ng = 0, ok = 1e9 + 1;
    // ok以下の硬貨がK枚以上
    while (ok - ng > 1) {
        int mid = (ok + ng) / 2;
        lint cnt = 0;
        for (int i = 0; i < N; ++i) {
            cnt += std::max(0, std::min(B[i], mid) - A[i] + 1);
        }

        (cnt >= K ? ok : ng) = mid;
    }

    std::cout << ok << std::endl;
    return 0;
}