#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,k;cin>>n>>k;
    int a[n],b[n];
    for(int i=0;i<n;i++){
        cin>>a[i]>>b[i];
    }
    int u=1000000001,d=1;
    while(u-d>1){
        int mid=(u+d)/2;
        long long sum=0;
        for(int i=0;i<n;i++){
            if(a[i]>mid)continue;
            sum+=min(b[i]+1,mid)-a[i];
        }
        if(sum>=k)u=mid;
        else d=mid;
    }
    cout<<d<<endl;
}