import java.util.*;

 class Solution{
	 public static void main(String args[]){
		 Scanner sc = new Scanner(System.in);
		 int n = sc.nextInt();
		 int a[][] = new int[n][n-1];
		 double t = 1.0 ;
		 
		 for(int i=0;i<n;i++){
			 for(int j=0;j<n-1;j++){
				 a[i][j] = sc.nextInt();
			 }
		 }
			 for(int i=0;i<n;i++){
				 for(int j=0;j<n-1;j++){
					 if(j==1){
						  t = t*a[i][j];
					 }
				 }
			 }
			 System.out.println(t/1000000);
		 }
		 
	 }