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

int N, K, A[100000], B[100000];

bool check(int C){
    int64_t sum = 0;
    for(int i=0; i<N; i++) sum += max(0, min(C, B[i]) - A[i] + 1);
    return (sum >= K);
}

int main(){
    cin >> N >> K;
    for(int i=0; i<N; i++) cin >> A[i] >> B[i];

    int ok = 1e9, ng = 0;
    while(ok-ng>1){
        int mid = (ok+ng)/2;
        (check(mid) ? ok : ng) = mid;
    }
    cout << ok << endl;
    return 0;
}