#include "bits/stdc++.h"
#define in std::cin
#define out std::cout
#define rep(i,N) for(LL i=0;i<N;++i)
typedef long long int LL;

int main()
{
	LL N, K;
	in >> N >> K;
	std::vector<LL>A(N), B(N);
	rep(i, N) in >> A[i] >> B[i];

	std::vector<LL>nums;
	std::map<LL, LL>index;
	rep(i, N)
	{
		nums.push_back(A[i]);
		nums.push_back(B[i] + 1);
	}
	std::sort(nums.begin(), nums.end());
	nums.erase(std::unique(nums.begin(), nums.end()), nums.end());
	rep(i, nums.size()) index[nums[i]] = i;

	std::vector<LL>imos(nums.size() + 1);
	rep(i, N)
	{
		++imos[index[A[i]]];
		--imos[index[B[i] + 1]];
	}
	rep(i, imos.size() - 1) imos[i + 1] += imos[i];

	LL cnt = 0;
	rep(i, imos.size() - 1)
	{
		LL left = nums[i], right = nums[i + 1] - 1;
		LL sum = imos[i] * (right - left + 1);
		if (cnt + sum >= K)
		{
			LL point = left + (K - cnt) / imos[i] + std::min<LL>((K - cnt) % imos[i], 1) - 1;
			out << point << std::endl;
			return 0;
		}
		cnt += sum;
	}
}