#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main(void) {
  int N; size_t K; scanf("%d%lu", &N, &K);
  vector<int> a(N), b(N);
  vector<int> v(N*2);
  for(int i=0, j=0; i<N; ++i) {
    scanf("%d%d", &a[i], &b[i]);
    v[j++] = a[i];
    v[j++] = b[i] + 1;
  }
  vector<int> w = v;
  sort(w.begin(), w.end()); w.erase(unique(w.begin(), w.end()), w.end());
  vector<size_t> per(N*2 + 1);
  for(int i=0, j=0; i<N; ++i) {
    size_t l = lower_bound(w.begin(), w.end(), v[j++]) - w.begin(),
           r = lower_bound(w.begin(), w.end(), v[j++]) - w.begin();
    ++per[l];
    --per[r];
  }
  for(int i=0; i<N*2; ++i) {
    per[i+1] += per[i];
  }
  size_t cnt = 0;
  for(size_t i=0, n=w.size(); i<n-1; ++i) {
    int range = w[i+1] - w[i];
    size_t ncnt = cnt + range * per[i];
    if(ncnt < K) {
      cnt = ncnt;
      continue;
    }
    size_t dif = K - cnt;
    size_t pos = (dif + per[i] - 1) / per[i];
    size_t res = pos + w[i] - 1;
    printf("%lu\n", res);
    return 0;
  }
  throw;
}