//1280
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<time.h>
int main(){
	int n;
	int m;
	int c;
	int i;
	int j,k;
	int pd;
	double pb;
	int count1=0,count2=0;
	int a[100000];
	int b[100000];
	printf("input n,m,c\n");
	scanf("%d %d %d",&n,&m,&c);
	printf("input a[i]\n");
	for(i=0;i<n;i++){
		scanf("%d",&a[i]);
	}
	printf("input b[i]\n");
	for(i=0;i<m;i++){
		scanf("%d",&b[i]);
	}
	for(j=0;j<n;j++){
		for(k=0;k<m;k++){
			pd=a[j]*b[k];
			if(pd>c){
				count1++;
			}
			else { 
				count2++;
			}
		}
	}
	pb=(double)count1/(count1+count2);
	printf("%lf",pb);
	system("pause");
}