#include <algorithm>
#include <cassert>
#include <cctype>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <vector>
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
//#define cerr if(false) cerr
#ifdef DEBUG
#define show(...) cerr << #__VA_ARGS__ << " = ", debug(__VA_ARGS__);
#else
#define show(...) 42
#endif
using namespace std;
using ll = long long;
using pii = pair<int, int>;
template <typename T, typename S>
ostream &operator<<(ostream &os, pair<T, S> a) {
    os << '(' << a.first << ',' << a.second << ')';
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> v) {
    for (auto x : v) os << x << ' ';
    return os;
}
template <typename T>
ostream &operator<<(ostream &os, set<T> v) {
    for (auto x : v) os << x << ' ';
    return os;
}
template <typename S, typename T>
ostream &operator<<(ostream &os, map<S, T> mp) {
    for (auto x : mp) os << x << ' ';
    return os;
}
void debug() {
    cerr << '\n';
}
template <typename H, typename... T>
void debug(H a, T... b) {
    cerr << a;
    if (sizeof...(b)) cerr << ", ";
    debug(b...);
}
int main() {
    int n, k;
    cin >> n >> k;
    vector<pii> d(n);
    rep(i, n) cin >> d[i].first >> d[i].second;
    int l = 0;
    int r = 1e9 + 2;
    while (r - l > 1) {
        int mid = (l + r) / 2;
        ll cnt = 0;
        rep(i, n) {
            if (d[i].first > mid) continue;
            if (d[i].second >= mid)
                cnt += mid - d[i].first + 1;
            else
                cnt += d[i].second - d[i].first + 1;
        }
        if (cnt >= k) {
            r = mid;
        } else {
            l = mid;
        }
    }
    cout << r << endl;
}