#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;

/*
*/

ll n,k,sum=0,tmp=0,before=1,ans;
map<ll,ll> m;


void init(){
	cin>>n>>k;
	rep(i,n){
		ll a,b;
		cin>>a>>b;
		m[a]++;
		m[b+1]--;
	}
}

int main(void){
	init();
	for(auto itr = m.begin(); itr != m.end(); ++itr) {
		if(sum+tmp*(itr->first-before)>=k){
			ans=before+ceil((double)(k-sum)/tmp)-1;
			break;
		}
		sum += tmp*(itr->first-before);
		tmp += itr->second;
		before = itr->first;
	}
	cout<<ans<<endl;
	return 0;
}