import java.util.Scanner;

public class Main {
	static int numerators[] = new int[100];

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	}

	static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	}

	static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	}

	static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	}

	static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	}

} import java.util.Scanner; Scanner java.util public class Main {
	static int numerators[] = new int[100];

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	}

	static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	}

	static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	}

	static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	}

	static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	}

} Main static int numerators[] = new int[100]; numerators new int[100] 100 public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int a[] = new int[n]; a new int[n] n for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			a[i] = sc.nextInt();
		} {
			a[i] = sc.nextInt();
		} a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc int lcm = getLcm(a); lcm getLcm(a) getLcm a calcNumerators(a, n, lcm) calcNumerators a n lcm int sum = java.util.Arrays.stream(numerators).sum(); sum java.util.Arrays.stream(numerators).sum() java.util.Arrays.stream(numerators).sum java.util.Arrays.stream(numerators) java.util.Arrays.stream java.util.Arrays java.util java java.util java.util.Arrays numerators double ans = (double) lcm / sum; ans (double) lcm / sum (double) lcm sum System.out.println(ans) System.out.println System.out System System.out ans String[] args args static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	} calcNumerators {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	} for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			numerators[i] = lcm / a[i];
		} {
			numerators[i] = lcm / a[i];
		} numerators[i] = lcm / a[i] numerators[i] numerators i lcm / a[i] lcm a[i] a i int a[] a int n n int lcm lcm static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	} getLcm {
		return m * n / getGcd(m, n);
	} return m * n / getGcd(m, n); m * n / getGcd(m, n) m * n m n getGcd(m, n) getGcd m n int m m int n n static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	} getLcm {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	} final int len = a.length; len a.length a a.length if (len == 1)
			return a[0]; len == 1 len 1 return a[0]; a[0] a 0 int l = getLcm(a[0], a[1]); l getLcm(a[0], a[1]) getLcm a[0] a 0 a[1] a 1 for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		} int i = 1; int i = 1; i 1 i < len - 1 i len - 1 len 1 i++ i++ i {
			l = getLcm(l, a[i + 1]);
		} {
			l = getLcm(l, a[i + 1]);
		} l = getLcm(l, a[i + 1]) l getLcm(l, a[i + 1]) getLcm l a[i + 1] a i + 1 i 1 return l; l int a[] a static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	} getGcd {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	} int temp; temp while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		} (temp = a % b) != 0 (temp = a % b) temp a % b a b 0 {
			a = b;
			b = temp;
		} a = b a b b = temp b temp return b; b int a a int b b public class Main {
	static int numerators[] = new int[100];

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	}

	static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	}

	static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	}

	static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	}

	static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	}

} public class Main {
	static int numerators[] = new int[100];

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	}

	static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	}

	static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	}

	static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	}

	static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	}

} Main
import java.util.Scanner;

public class Main {
	static int numerators[] = new int[100];

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}
		int lcm = getLcm(a);
		calcNumerators(a, n, lcm);
		int sum = java.util.Arrays.stream(numerators).sum();
		double ans = (double) lcm / sum;
		System.out.println(ans);
	}

	static void calcNumerators(int a[], int n, int lcm) {
		for (int i = 0; i < n; i++) {
			numerators[i] = lcm / a[i];
		}
	}

	static int getLcm(int m, int n) {
		return m * n / getGcd(m, n);
	}

	static int getLcm(int a[]) {
		final int len = a.length;
		if (len == 1)
			return a[0];

		int l = getLcm(a[0], a[1]);
		for (int i = 1; i < len - 1; i++) {
			l = getLcm(l, a[i + 1]);
		}
		return l;
	}

	static int getGcd(int a, int b) {
		int temp;
		while ((temp = a % b) != 0) {
			a = b;
			b = temp;
		}
		return b;
	}

}
