#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
#include <cassert>
#include <complex>
using namespace std;
#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;
const int inf = 1e8;

vector<int>a,b;
int n;
ll k;

bool check(int x){
    ll num = 0;
    for(int i=0;i<n;i++){
        if(a[i]>x)continue;
        if(a[i]==x){
            num++;
            continue;
        }
        if(b[i]<x){
            num+=b[i]-a[i]+1;
            continue;
        }
        if(a[i]<=x && x<=b[i]){
            num+=x-a[i]+1;
            continue;
        }
    }
    return num>=k;
}

int main() {
    cin>>n>>k;
    a.resize(n),b.resize(n);
    int ng = -1,ok = 0;
    for(int i=0;i<n;i++){
        cin>>a[i]>>b[i];
        ok = max(ok,b[i]);
    }
    while(ok-ng>1){
        int mid = (ok+ng)/2;
        if(check(mid))ok = mid;
        else ng = mid;
    }
    cout<<ok<<endl;
}