#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; 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);
	rep(i, n) {
		cin >> a[i] >> b[i];
	}
	int ng = -1;
	int ok = INF + 1;
	while (1 < abs(ok - ng)) {
		int mid = (ng + ok) / 2;
		auto check = [&]() {
			long long x = 0;
			rep(i, n) {
				if (mid < a[i])continue;
				x += min(mid, b[i]) - a[i] + 1;
			}
			return x >= k;
		};
		if (check()) ok = mid;
		else ng = mid;
	}
	cout << ok << endl;

	return 0;
}