#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vmi = vector<mint>;
using vvmi = vector<vmi>;
using vvvmi = vector<vvmi>;
#define all(a) (a).begin(), (a).end()
#define rep2(i, m, n) for (int i = (m); i < (n); ++i)
#define rep(i, n) rep2(i, 0, n)
#define drep2(i, m, n) for (int i = (m)-1; i >= (n); --i)
#define drep(i, n) drep2(i, n, 0)

void solve(){
    
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n; ll k; cin >> n >> k;
    vll a(n), b(n); rep(i, n)cin >> a[i] >> b[i];
    ll l = 0, r = 1e9+1;
    ll mid;
    while(r-l>1){
        mid = (l+r)/2;
        ll c = 0;
        rep(i, n){
            if(mid < a[i])continue;
            c += min(mid, b[i]) - a[i]+1;
        }
        if(c < k){
            l = mid;
        }else{
            r = mid;
        }
    }cout << r << endl;

    return 0;
}