#include<bits/stdc++.h>
using namespace std;
#define REP(i,m,n) for(int i=(int)(m) ; i < (int) (n) ; ++i )
#define rep(i,n) REP(i,0,n)
typedef long long ll;

int main(){
    int n,k;
    cin>>n>>k;
    assert(1<=n&&n<=100000);
    assert(1<=k&&k<=1000000000);
    int l[n],r[n];
    ll sum=0;
    rep(i,n){
        cin>>l[i]>>r[i];
        sum+=r[i]-l[i]+1;
        assert(1<=l[i]&&l[i]<=r[i]&&r[i]<=1000000000);
    }
    assert(k<sum);
    int ok=1e9+7,ng=0;
    while(ok-ng>1){
        int mid=(ok+ng)/2;
        ll cnt=0;
        rep(i,n){
            if(l[i]>mid)continue;
            cnt+=min(r[i],mid)-l[i]+1;
        }
        if(cnt>k)ok=mid;
        else ng=mid;
    }
    cout<<ok<<endl;
    return 0;
}