import java.util.*

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    val n = scanner.nextInt()
    val array = Array(n, {0.0})
    for(i in 0..n-1){
        array[i] = scanner.nextDouble()
    }
    var gcd = array[0]
    for(i in 1..n-1){
        gcd = gcd * array[i] / cal(gcd, array[i])
    }
    var sum = 0.0
    for(i in 0..n-1){
        sum += gcd / array[i]
    }
    println(gcd / sum)
}

fun cal(x:Double, y:Double): Double{
    var x2 = x;
    var y2 = y;
    if(x2 < y2) return cal(y2, x2);
    if(y2 === 0.0) return x2;
    return cal(y2, x2 % y2);
}