import java.util.*;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	}
} import java.util.*; util.* java import java.math.BigInteger; BigInteger java.math public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	}
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	} main {
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc BigInteger sum =  BigInteger.valueOf(0); sum BigInteger.valueOf(0) BigInteger.valueOf BigInteger 0 BigInteger bi = BigInteger.valueOf(1); bi BigInteger.valueOf(1) BigInteger.valueOf BigInteger 1 int[] list = new int[n]; list new int[n] n for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        } {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        } int value = sc.nextInt(); value sc.nextInt() sc.nextInt sc list[i] = value list[i] list i value bi = bi.multiply(BigInteger.valueOf(value)) bi bi.multiply(BigInteger.valueOf(value)) bi.multiply bi BigInteger.valueOf(value) BigInteger.valueOf BigInteger value for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        } {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        } BigInteger bi2 = BigInteger.valueOf(1); bi2 BigInteger.valueOf(1) BigInteger.valueOf BigInteger 1 for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          } int count = 0; int count = 0; count 0 count < n count n count++ count++ count {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          } {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          } if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            } i != count i count {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            } bi2 = bi2.multiply(BigInteger.valueOf(list[count])) bi2 bi2.multiply(BigInteger.valueOf(list[count])) bi2.multiply bi2 BigInteger.valueOf(list[count]) BigInteger.valueOf BigInteger list[count] list count sum = sum.add(bi2) sum sum.add(bi2) sum.add sum bi2 BigInteger[] ans = bi.divideAndRemainder(sum); ans bi.divideAndRemainder(sum) bi.divideAndRemainder bi sum double seisu = ans[0].doubleValue(); seisu ans[0].doubleValue() ans[0].doubleValue ans[0] ans 0 double amari = ans[1].doubleValue(); amari ans[1].doubleValue() ans[1].doubleValue ans[1] ans 1 double bunbo = sum.doubleValue(); bunbo sum.doubleValue() sum.doubleValue sum double shousu = amari / bunbo; shousu amari / bunbo amari bunbo System.out.println(seisu + shousu) System.out.println System.out System System.out seisu + shousu seisu shousu String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	}
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	}
} Main
import java.util.*;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
    
		// 整数の入力
		int n = sc.nextInt();
        BigInteger sum =  BigInteger.valueOf(0);
        BigInteger bi = BigInteger.valueOf(1);
        int[] list = new int[n];
        for (int i = 0; i < n; i++) {
          int value = sc.nextInt();
          list[i] = value;
          bi = bi.multiply(BigInteger.valueOf(value));
        }
        for (int i = 0; i < n; i++) {
          BigInteger bi2 = BigInteger.valueOf(1);
          for (int count = 0; count < n; count++) {
            if (i != count) {
              bi2 = bi2.multiply(BigInteger.valueOf(list[count]));
            }
          }
          sum = sum.add(bi2);
        }
        BigInteger[] ans = bi.divideAndRemainder(sum);
        double seisu = ans[0].doubleValue();
        double amari = ans[1].doubleValue();
        double bunbo = sum.doubleValue();
        double shousu = amari / bunbo;
        
        System.out.println(seisu + shousu);
	}
}