#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define P pair<int, int>

#define MOD 1000000007
#define INF 2147483647
#define NINF (-2147483647-1)
#define LLINF 9223372036854775807
using ll = long long;
using namespace std;

int main() {
    int K, N;
    cin >> N >> K;
    vector<P> A(N);
    for (int i = 0; i < N; i++)
    {
        cin >> A[i].first >> A[i].second;
    }
    int left = 0, right = INF;
    while (left < right - 1) {
        int mid = (left + right) / 2;
        ll cnt = 0;
        for (int i = 0; i < N; i++)
        {
            if (A[i].first > mid) continue;
            if (A[i].second > mid) {
                cnt += mid - A[i].first + 1;
            }
            else {
                cnt += A[i].second - A[i].first + 1;
            }
        }
        if (cnt >= K) {
            right = mid;
        }
        else {
            left = mid;
        }
    }
    cout << right << endl;
    getchar(); getchar();
    return 0;
}