#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

int main(){
	
	int N;
	long long K;
	cin>>N>>K;
	
	vector<int> A(N),B(N);
	rep(i,N)scanf("%d %d",&A[i],&B[i]);
	
	int ok = 0,ng = 1000000001;
	
	while(ng-ok>1){
		int mid = (ok+ng)/2;
		long long sum = 0LL;
		rep(i,N){
			if(B[i]<=mid)sum += B[i]-A[i]+1;
			else if(A[i]>mid)continue;
			else{
				sum += mid-A[i]+1;
			}
		}
		
		if(sum<K)ok = mid;
		else ng = mid;
	}
	
	cout<<ok+1<<endl;
	
	return 0;
}