#include <iostream>
using namespace std;
int a[100001];
void rendez(int n,int a[]) {
    for (int i = 0; i < n - 1; i++) {
        for (int j = i + 1; j < n; j++) {
            if (a[i] > a[j]) {
                swap(a[i], a[j]);
            }
        }
    }
}
int main()
{
    int n, m, k;
    cin >> n >> m >> k;
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    rendez(n, a);
    int x = 0;
    while (a[x] < 0) {
        x++;
    }
    if (x > k) {
        while (x > k && m>0) {
            x--;
            m -= abs(a[x]);
            a[x] = 0;
        }
        
    }
    while (m) {
        int i = x+1;
        a[x]++;
        m--;
        while (a[i] < a[x] && m && i<n) {
            a[i]++;
            m--;
            i++;
        }
    }
    int s = 1;
    for (int i = 0; i < n; i++) {
        s *= a[i];
    }
    if (x > k) {
        cout << -1;
    }
    else {
        cout << s;
    }
    

}