#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
#include<map>
#include<stack>
#include<cmath>
#include<iomanip>
#include<set>
#include<numeric>
#include<sstream>
#include<random>
#include<cassert>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rrep(i, st, n) for (int i = st; i < n; ++i)
using pii = pair<int, int>;
const int inf = 1e9 + 7;
int dy[] = {0, 0, -1, 1, -1, 1, -1, 1};
int dx[] = {1, -1, 0, 0, -1, 1, 1, -1};
#define ceil(a, b) a / b + !!(a % b)

int main() {
    int n, k;
    cin >> n >> k;
    int a[n], b[n];
    rep(i, n) cin >> a[i] >> b[i];
    int l = 1, r = 1e9 + 1;
    int cou = 0;
    while (l + 1 < r) { //break when l + 1 = r
        cou++;
        if (cou > 300) break;
        int mid = (l + r) / 2;
        //cout << l << " " << mid << " " << r << endl;
        ll c = 0;
        rep(i, n) { //何枚がmid円以下か
            c += (ll)max(0, min(mid, b[i]) - a[i] + 1);
        }
        //cout << c << endl;
        if (c >= k) { //足りてるから数字大きくする
            r = mid + 1;
        } else { //足りない
            l = mid;
        }
        //cout << l << " " << mid << " " << r << endl;
    }
    cout << l + 1 << endl;
}