#include<stdio.h>
#include<limits.h>
#define min(a,b) (a<b?a:b)
typedef long long ll;
int N,K,A[101010],B[101010];
int check(int x){
  ll cnt=0;
  for(int i=0;i<N;i++){
    if(A[i]<=x){
      cnt+=min(B[i],x)-A[i]+1;
    }
  }
  return K<=cnt;
}
int main(void){
  scanf("%d%d",&N,&K);
  for(int i=0;i<N;i++) scanf("%d%d",&A[i],&B[i]);
  int ng=0,ok=INT_MAX;
  while(ng+1!=ok){
    int md=(ok+ng)/2;
    if(check(md)) ok=md;
    else ng=md;
  }
  printf("%d",ok);
}