#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
string bin(unsigned  long long  x){
    string odp="";
    while(x>0){
        if(x%2 == 0){
            odp+='0';
            //odp = '0'+odp;
        }else{
            //odp='1'+odp;
            odp+='1';
        }
        x/=2;
    }
    int p = 31 - odp.size();
    for(int i=0; i<p; i++){
        odp+='0';
    }
    return odp;
}
unsigned long long dec(string x){
    unsigned long long odp =0;
    unsigned long long dwa = 1;
    for(int i=30; i>=0; i--){
        if(x[i] =='1'){
            odp+=dwa;
        }
        dwa*=2;
    }

    return odp;
}
int main() {
    ios_base::sync_with_stdio(false);

    int n;
    int k;
    vector<unsigned long long> v;
    unsigned  long long x;
    cin >> n >> k;
    unsigned long long maks = 0;
    for(int i = 0 ; i < n; i++)
    {
        cin >> x;
        v.push_back(x);
        if(x > maks) maks = x;
    }

    if(k == 1)
    {
        cout << maks << endl;
    }
    else
    {
        sort(v.begin(), v.end());
        vector<string> tab(n);
        for(int i=0; i<n; i++){
            tab[i] = bin(v[i]);
        }
        int z=0;
        string s_odp ="";
        for(int j=30; j>=0; j--) {
            int ILE_JEDYNEK = 0;
            int nz=0;
            for (int i = n-1; i >= z; i--) {
                //cout<<i<<" "<<j<<" i j ";
               // cout<<z<<" <-z"<<tab[i][j]<<" tabij\n";
                if(tab[i][j]!='1'){

                }else{
                    nz=i;
                    ILE_JEDYNEK++;
                }
            }
            if(ILE_JEDYNEK <k){
                s_odp+='0';
            }else{
                s_odp+='1';
                z = nz;
                //cout<<"ZZ "<<z<<"\n";

            }
        }

        //cout<<s_odp<<"\n";
        cout<<dec(s_odp)<<"\n";


    }

    return 0;
}