//
//
//  Codeforces: ganariya
//  AtCoder: ganariya2525
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//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//~~~~~~~~~~~~~~~~~~~~~_(＾～＾ ｣ ∠)_~~~~~~~~~~~~~~~~~~~~~

bool isGood(LL N, LL K, LL mid, vector<LL> &A, vector<LL> &B) {
    LL sum = 0;
    for (int i = 0; i < N; i++) {
        if (B[i] <= mid) {
            sum += (B[i] - A[i] + 1);
            continue;
        }
        if (mid < A[i])continue;
        sum += mid - A[i] + 1;
    }
    return sum >= K;
}

int main() {

    LL N, K;
    cin >> N >> K;

    vector<LL> A(N), B(N);
    for (int i = 0; i < N; i++) cin >> A[i] >> B[i];

    LL ng = 0;
    LL ok = 1000000010LL;

    while (abs(ok - ng) > 1) {
        LL mid = (ok + ng) / 2;
        if (isGood(N, K, mid, A, B)) ok = mid;
        else ng = mid;
    }

    cout << ok << endl;

    return 0;
}