#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> l_l;

#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))
//const ll mod = 1000000007;

int main() {
    //cout.precision(10);
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, K;
    cin >> N >> K;
    K++;
    int A[100500];
    int B[100500];
    for(int i = 1; i <= N; i++) cin >> A[i] >> B[i];
    int ok = INF;
    int ng = 0;
    while(ok - ng > 1) {
        int mid = (ok + ng) / 2;
        int now = 0;
        for(int i = 1; i <= N; i++) {
            int NEW = min(B[i], mid) - A[i] + 1;
            now += max(0, NEW);
            if(now >= K) break;
        }
        if(now >= K) ok = mid;
        else ng = mid;
    }
    cout << ok << endl;
    return 0;
}