/**Lucky Boy**/
#include <bits/stdc++.h>
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for (int i = (a); i >= (b); --i)
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define maxc 1000000007
#define maxn 500005
#define maxm 500005
#define pii pair <int,int>
#define Task "Karte"
template <typename T> inline void read(T &x){char c;bool nega=0;while((!isdigit(c=getchar()))&&(c!='-'));if(c=='-'){nega=1;c=getchar();}x=c-48;while(isdigit(c=getchar())) x=x*10+c-48;if(nega) x=-x;}
template <typename T> inline void writep(T x){if(x>9) writep(x/10);putchar(x%10+48);}
template <typename T> inline void write(T x){if(x<0){putchar('-');x=-x;}writep(x);putchar(' ');}
template <typename T> inline void writeln(T x){write(x);putchar('\n');}
using namespace std;
int n,k,a[maxn << 1],cnt;
int Calc(int x)
{
int cnt = 0;
FOR(i,0,n-1) if (cnt < a[i+x]) ++cnt;
return cnt;
}
int main()
{
//ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//freopen(Task".inp", "r",stdin);
//freopen(Task".out", "w",stdout);
read(n),read(k);
FOR(i,1,n) read(a[i]);
sort(a+1,a+n+1);
FOR(i,1,n) a[i+n] = a[i];
int l = 1,r = n + 1;
while (r - l > 1)
{
int mid = (l+r) >> 1;;
if (Calc(mid) >= k) l = mid;
else r = mid;
}
if (Calc(l) == k) FORD(i,n-1,0) write(a[i+l]);
else write(-1);
return 0;
}
