#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
using namespace std;

using ll = long long;
using P = pair<int, int>;
constexpr int INF = 1001001001;
constexpr int mod = 1000000007;
// constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    int N, K;
    cin >> N >> K;
    vector<int> A(N), B(N);
    for(int i = 0; i < N; ++i)  cin >> A[i] >> B[i];
    
    int lb = 0, ub = 1e+9;
    while(ub - lb > 1){
        int mid = (lb + ub) / 2;
        ll cnt = 0;
        for(int i = 0; i < N; ++i){
            cnt += max(0, min(B[i], mid) - A[i] + 1);
        }
        if(cnt >= K)    ub = mid;
        else    lb = mid;
    }

    cout << ub << '\n';

    return 0;
}