#include <iostream>
#include <algorithm>
#include <cstring>
using namespace std;
const int N = 1025;

//快读
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 << 3) + (x << 1) + (ch ^ 48);
        ch = getchar();
    }
    return x * f;
}

//树状数组
int tr[N];
void add(int x, int c) {
    for (; x < N; x += x & -x) tr[x] += c;
}
//查询x的个数和
int getSum(int x) {
    int sum = 0;
    for (; x; x -= x & -x) sum += tr[x];
    return sum;
}

//从1开始查找第k小的数
int getKth(int k) {
    int l = 1, r = N - 1; //保证数组不能越界
    while (l < r) {
        int mid = (l + r) >> 1;
        if (getSum(mid) >= k)
            r = mid;
        else
            l = mid + 1;
    }
    return l;
}
/*
测试用用例:
2 9 1 3 12 7 6 -1
3

答案：
3
*/
int main() {
    int x;
    while (x = read(), ~x) add(x, 1); // x这个位置上+1
    int k = read();
    printf("%d\n", getKth(k));
    return 0;
}