#include <iostream>
using namespace std;
typedef long long ll;
int main(){
    int n;ll k;
    cin>>n>>k;
    ll a[100001], b[100001];
    for(int i=0; i<n; i++){
        cin>>a[i]>>b[i];
    }
    ll x1=0, x2=1e9+7;
    while(x1!=x2){
        ll x=(x1+x2)/2;
        ll c=0;
        for(int i=0; i<n; i++){
            if(x<a[i]) continue;
            if(x>=b[i]){
                c+=(b[i]-a[i]+1);
            }else{
                c+=(x-a[i]+1);
            }
        }
        if(c<k) x1=x+1;
        else x2=x;
    }
    cout<<x1<<endl;
    return 0;
}