public class binsearch {
    // suche x in elems und gib dessen Index zurueck, sonst -1
    // elems muss aufsteigend sortiert sein; Klasse beliebig
    public static int index (int x, int[] elems) {
        int i = 0;
        int j = elems.length-1;
        while (i<=j) {
            int k = i+((j-i) / 2);
            if (x < elems[k]) {
                j = k-1;
            } else if (x == elems[k]) {
                return k;
            } else {
                i = k+1;
            }
        }
        return -1;
    }
    
    // Aufruf: java binsearch <key> <elem> <elem> <elem>
    // z.B.: java binsearch 10 38 27 43 3 9 82 10
    public static void main(String [] args) {
        int[] elems = new int[args.length-1];
        for (int i=1; i<args.length; i++)
            elems[i-1] = Integer.parseInt(args[i]);
        sort.mergesort(elems);
        System.out.println(index(Integer.parseInt(args[0]),elems));
    }
}