#include <iostream>
#include <map>
#include <vector>
using namespace std;
int main(){
  long long n,k;cin>>n>>k;
  map<int,long long> A;
  for(int i = 0; n > i; i++){
    int a,b;cin>>a>>b;
    A[a]++;
    A[b+1]--;
  }
  int prev = -1;
  long long nw = 0;
  long long pres = 0;
  for(auto x: A){
    if((x.first-prev)*nw + pres >= k){
      cout << prev+(k-pres)/nw << endl;
      return 0;
    }
    pres += (x.first-prev)*nw;
    nw += x.second;
    prev = x.first;
  }
}