#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=144499999994;
ll mod=1000000007;
int main(){
    ll n,k;
    cin >> n >> k;
    vector<ll>a(n),b(n);
    for (ll i = 0; i < n; i++)
    {
        cin >> a[i] >> b[i];
    }
    ll left=0,right=inf;
    while (right-left>1)
    {
        ll mid=(right+left)/2;
        ll x=0;
        for (ll i = 0; i < n; i++)
        {
            if (mid>=a[i])
            {
                if (mid>=b[i])
                {
                    x+=b[i]-a[i]+1;
                }else{
                    x+=mid-a[i]+1;
                }
            }
        }
        if (x<k)
        {
            left=mid;
        }else{
            right=mid;
        }
    }
    cout << right << endl;
}