#include<bits/stdc++.h>
using namespace std;

inline int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9'){
        if(ch=='-') f=-1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9'){
        x=x*10+ch-48;
        ch=getchar();
    }
    return x*f;
}
int n,m,k;
int a[101010];

int check(int x){
    if(x<0) return 0;
    int t=k+a[x];
    vector<int> v;
    int i;
    for(int i=0;i<n;i++){
        if(i!=x) v.push_back(a[i]);
    }
    int ret=0;
    int l=0,r=v.size()-1;
    while(l<r){
        while(l<r && v[r]+v[l]<=t) l++;
        if(l>=r) break;
        ret++;
        l++,r--;
    }
    return ret<m;
}

signed main(){
//  freopen("","r",stdin);
//  freopen("","w",stdout);
    cin>>n>>m;
    cin>>k;
    for(int i=0;i<n-1;i++){
        a[i]=read();
    }
    n--;
    sort(a,a+n);
    int x=n-1;
    if(check(x)==0){
    	printf("-1\n");
    	return 0;
	}
    for(int i=20;i>=0;i--){
        if(check(x-(1<<i))){
            x-=1<<i;
        }
    }
    cout<<a[x]<<endl;
    return 0;
}