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

int main() {
  ios::sync_with_stdio(false);

  int N, K; {
    cin >> N >> K;
  }

  vector<int> A(N), B(N); {
    for (int i = 0; i < N; ++i) cin >> A[i] >> B[i];
  }

  int lb = 0;
  int ub = 1e9;
  while (ub - lb > 1) {
    int mb = lb + ub >> 1;
    int64_t c = 0;
    for (int i = 0; i < N; ++i) {
      c += max(0, min(B[i] - A[i] + 1, mb - A[i] + 1));
    }
    (c >= K ? ub : lb) = mb;
  }

  cout << ub << endl;
}