#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

int main() {
  int N;
  long long K;
  cin >> N >> K;
  vector<int> A(N), B(N);
  long long s = 0;
  for (int i = 0; i < N; i++) {
    cin >> A[i] >> B[i];
    B[i]++;
    s += B[i] - A[i];
  }
  int l = 0;
  int r = (int)1e9 + 1;
  while (r - l > 1) {
    int m = (l + r) / 2;
    long long c = 0;
    for (int i = 0; i < N; i++) {
      c += max(0, m - A[i]);
      c -= max(0, m - B[i]);
    }
    if (c >= K) {
      r = m;
    } else {
      l = m;
    }
  }
  cout << l << endl;
}