/* ---------- STL Libraries ---------- */
// IO library
#include <cstdio>
#include <fstream>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm library
#include <algorithm>
#include <cmath>
#include <numeric>
#include <random>
#include <cstring>

// container library
#include <array>
#include <bitset>
#include <deque>
#include <map>
#include <unordered_map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>
#include <stack>

/* ---------- Namespace ---------- */
using namespace std;

/* ---------- Type ---------- */
using ll = long long;
#define int ll
#define P pair<ll, ll>

/* ---------- Constants  */
const double PI = 3.141592653589793238462643383279;
const ll MOD = 1e9 + 7;
const int INF = 1LL << 55;

const int MAX_N = 100000;
int N, K;
int A[MAX_N];
int B[MAX_N];

bool f(int x) {
    int num = 0;
    for (int i = 0; i < N; i++) {
        num += max(0LL, min(x, B[i]) - A[i] + 1);
    }
    return num >= K;
}

signed main() {
    cin >> N >> K;
    for (int i = 0; i < N; i++) cin >> A[i] >> B[i];
    int lb = 0;
    int ub = INF;
    while (ub - lb > 1) {
        int mid = (ub + lb) / 2;
        if (f(mid)) {
            ub = mid;
        } else {
            lb = mid;
        }
    }
    cout << ub << endl;
    return 0;
}