#include <bits/stdc++.h>
#define rep(i, a, n) for(int i = a; i < n; i++)
#define int long long
using namespace std;
typedef pair<int, int> P;
const int mod = 1000000007;
const int INF = 1e18;

int n, k;
vector<int> a, b;

bool f(int mid){
    int sum = 0;
    rep(i, 0, n){
        if(a[i] <= mid && mid <= b[i]){
            sum += mid - a[i] + 1;
        }else if(b[i] < mid){
            sum += b[i] - a[i] + 1;
        }
    }
    return sum >= k;
}

signed main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> n >> k;
    a.resize(n); b.resize(n);
    rep(i, 0, n){
        cin >> a[i] >> b[i];
    }
    int ok = *max_element(b.begin(), b.end());
    int ng = 0;
    while(ok - ng > 1){
        int mid = (ok + ng) / 2;
        if(f(mid)) ok = mid;
        else ng = mid;
    }
    cout << ok << endl;
}