#include<iostream>
#include<vector>
#include<algorithm>
#include<queue>
using namespace std;
int N,K;
vector<pair<int,int> >A;
main()
{
	cin>>N>>K;
	for(int i=0;i<N;i++)
	{
		int a,b;cin>>a>>b;
		A.push_back({a,b});
	}
	int L=0,R=1e9+114514;
	while(R-L>1)
	{
		int M=(L+R)/2;
		int now=K;
		for(int i=0;i<N;i++)
		{
			if(A[i].first<=M)
			{
				now-=min(M,A[i].second)-A[i].first+1;
				if(now<=0)break;
			}
		}
		if(now<=0)R=M;
		else L=M;
	}
	cout<<R<<endl;
}