#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

template <class F>
int lower_bound(int i0, int i1, F f) {
    while (i0 < i1) {
        int i = (i0 + i1) / 2;
        if (f(i)) i1 = i; else i0 = i + 1;
    }
    return i0;
}

struct P {
    int a, b;
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, k;
    cin >> n >> k;

    vector<P> p(n);
    for (int i = 0; i < n; i++) {
        int a, b;
        cin >> a >> b;
        p[i] = { a, b + 1 };
    }

    //c円以下のものがk枚あるか 満たす中で最も小さいもの
    int c = lower_bound(1, 1 << 30, [&](int c) {
        ll s = 0;
        for (int i = 0; i < n; i++) {
            if (c < p[i].a) continue;
            if (c < p[i].b) s += c + 1 - p[i].a; else s += p[i].b - p[i].a;
        }
        return s >= (ll)k;
    });

    cout << c << endl;

    return 0;
}