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


int main() {
    ll N, K;
    cin >> N >> K;
    ll A[N];
    ll B[N];
    rep(i, N) {
        cin >> A[i];
        cin >> B[i];
        B[i]++;
    }
    sort(A, A + N);
    sort(B, B + N);

    int aidx = 0;
    int bidx = 0;
    ll diff = 0;
    ll last = 0;
    ll count = 0;
    while (true) {
        if (aidx >= N || B[bidx] <= A[aidx]) {
            ll c2 = count + (B[bidx] - last) * diff;
            if (c2 >= K) {
                ll dd = (K - count - 1) / diff;
                ll ans = last + dd;
                cout << ans << endl;
                break;
            }
            count = c2;
            diff--;
            last = B[bidx];
            bidx++;
            if (bidx >= N) {
                break;
            }
        } else {
            ll c2 = count + (A[aidx] - last) * diff;
            if (c2 >= K) {
                ll dd = (K - count - 1) / diff;
                ll ans = last + dd;
                cout << ans << endl;
                break;
            }
            count = c2;
            diff++;
            last = A[aidx];
            aidx++;
        }
    }

    return 0;
}