#include <iostream>
using namespace std;
typedef long long ll;
ll N,K;
ll A[100010],B[100010];
int main(){
    cin >> N >> K;
    for(int i=1;i<=N;i++){
        cin >> A[i] >> B[i];
    }
    int l = 0,r = 1e9+1;
    while(l+1<r){
        int m = (l+r)/2;
        ll cnt = 0;
        for(int i=1;i<=N;i++){
            if(m<A[i]) continue;
            cnt += min(m-A[i]+1,B[i]-A[i]+1);
        }
        if(cnt<K) l = m;
        else r = m;
    }
    cout << r << endl;
}