#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define out(a) cout << a << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)

int main() {
    int n, k; cin >> n >> k;
    vector<pii> v;
    int rmax = -inf;
    rep(i, n) {
        int a, b; cin >> a >> b;
        v.eb(a, b);
        chmax(rmax, b);
    }
    int l = 1, r = rmax; //l, r閉区間
    while (1) {
        int mid = (l + r) / 2;
        int cnt = 0;
        rep(i, n) {
            if (mid - v[i].F < 0) continue;
            cnt += min(v[i].S, mid) - v[i].F + 1;
            if (cnt >= k) break;
        }
        //out(l << " " << r << " " << mid << " " << cnt);
        if (cnt >= k) r = mid;
        else l = mid;
        if (l + 1 == r) {
            out(r);
            return 0;
        }
    }
    
}