#include 	<stdio.h>
#include <math.h>
#define ZERO 0
#define BAD 1
int vvod(int *a, int *n)
{
    char sp = ' ';
    int ch_s = 0;
    int ch;
    int i = 0;
    scanf("%d", n);
    if ((*n == 0) || (*n > 10))
        return BAD;
    else
    {
        while (i < *n && sp != '\n')
        {
            ch = scanf("%d%c", &a[i], &sp);
            if (sp != '\n' && ch != EOF)
                ch_s ++;
            i++;
        }
        if (ch_s != (*n) - 1)
            return BAD;
        else
	    return ZERO;
    }
}
float srednee(int *a, int n)
{
    float x = 1;
    float mg;
    int i;
    float power;
    float positiv_n = 0;
    for (i = 0; i < n; i++)
    {
        if (a[i] >= 0)
        {
            x = x * a[i];
            positiv_n += 1;
        }
    }
    if (positiv_n == 0)
        mg = -1;
    else
    {
        power = 1 / positiv_n;
        mg = pow(x, power);
    }
    return mg;
}
int main()
{
    int a[10];
    int n;
    int x;
    float res;
    x = vvod(a, &n);
    res = srednee(a, n);
    if (x == 1)
	return BAD;
    else if (res < 0)
        return BAD;
    else
    {
        printf("%f", res);
        return ZERO;
    }
}