import java.util.*;
import java.lang.*;
import java.io.*;


class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        
        int p1 = Integer.parseInt(st.nextToken());
        int p2 = Integer.parseInt(st.nextToken());
        int p3 = Integer.parseInt(st.nextToken());
        int k = Integer.parseInt(st.nextToken());

        PriorityQueue<Long> pq = new PriorityQueue<>(); 
        int a = 1;
        int b = 1;
        int c= 1;
        for (int i=0; i<10; i++) {
            a *= p1;
            b=1;
            for (int j=0; j<10; j++) {
                b *= p2;
                c=1;
                for (int l=0; l<10; l++) {
                    c *= p3;
                    pq.add((long)a*b*c);
                }
        }
    }
        for (int i=0; i<k-1; i++) {
            pq.poll();
        }
        System.out.println(pq.poll());
}
}