#include<bits/stdc++.h>
using namespace std;
using ll = long long;

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl

ll N, K;
vector<ll> A;
vector<ll> B;

// yen円までに何枚あるか
ll calc_count(ll yen){
    ll count = 0;
    FOR(i, 0, N){
        if(B[i]<=yen){
            count += B[i]-A[i]+1;
        }
        // B > yen
        else{
            if(A[i]<=yen){
                count += yen-A[i]+1;
            }
        }
    }
    return count;
}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    cin >> N >> K;
    A.resize(N);
    B.resize(N);

    FOR(i, 0, N){
        cin >> A[i] >> B[i];
    }

    ll left = 0;
    ll right = 1e9;
    while(left+1!=right){
        ll center = (left+right)/2;
        ll count = calc_count(center);
        if(count>=K){
            right = center;
        }else{
            left = center;
        }
    }

    p(right);
    
    return 0;
}