#include <bits/stdc++.h>
using namespace std;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using P = pair<ll, ll>;
const long double PI = acos(-1.0L);
ll GCD(ll a, ll b) { return b?GCD(b, a%b):a; }
ll LCM(ll a, ll b) { return a/GCD(a, b)*b; }

int main() {
    ll n, k; cin >> n >> k;
    vector<ll> avec(n, 0);
    vector<ll> bvec(n, 0);
    for(int i = 0; i < n; ++i) {
        cin >> avec[i] >> bvec[i];
    }

    ll ok = 1e9; ll ng = 0;
    while(abs(ok-ng) > 1) {
        ll mid = (ok+ng)/2;
        auto isOK = [&](ll key) {
            // n個の幅についてチェックしていく
            ll cnt = 0;
            for(int i = 0; i < n; ++i) {
                if(avec[i] <= key) {
                    if(bvec[i] <= key) {
                        cnt += (bvec[i]-avec[i]+1);
                    }else {
                        cnt += (key-avec[i]+1);
                    }
                }
            }
            if(cnt >= k) return true;
            else return false;
        };
        if(isOK(mid)) ok = mid;
        else ng = mid;
    }
    cout << ok << endl;
}