#include<bits/stdc++.h>
using namespace std;

int main(){
    unsigned long N, K;
    cin >> N >> K;
    vector<pair<unsigned long, unsigned long>> donation(N);
    for(auto& i : donation)cin >> i.first >> i.second, ++i.second;
    auto cnt = [&donation, &K](unsigned long T){
        unsigned long ret{0};
        for(auto i : donation)ret += min(T, i.second) - min(T, i.first);
        return ret;
    };
    unsigned long l = 0, r = 1000000001;
    while(l + 1 < r){
        auto m = (l + r) / 2;
        (cnt(m) >= K ? r : l) = m;
    }
    cout << l << endl;
}