#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <float.h>

double minCost;

void generateCombinations(int* quality, int* wage, int n, int k, int start, int* current, int currentSize) {
    if (currentSize == k) {
        double maxRatio = 0;
        int totalQuality = 0;
        
        for (int i = 0; i < k; i++) {
            double ratio = (double)wage[current[i]] / quality[current[i]];
            if (ratio > maxRatio) maxRatio = ratio;
            totalQuality += quality[current[i]];
        }
        
        double cost = maxRatio * totalQuality;
        if (cost < minCost) minCost = cost;
        return;
    }
    
    for (int i = start; i < n; i++) {
        current[currentSize] = i;
        generateCombinations(quality, wage, n, k, i + 1, current, currentSize + 1);
    }
}

double solution(int* quality, int* wage, int n, int k) {
    minCost = DBL_MAX;
    int* current = (int*)malloc(k * sizeof(int));
    generateCombinations(quality, wage, n, k, 0, current, 0);
    free(current);
    return minCost;
}

int main() {
    char line[1000];
    fgets(line, sizeof(line), stdin);
    
    int quality[100], wage[100];
    int n = 0;
    
    char* token = strtok(line + 1, ",]");
    while (token != NULL) {
        quality[n++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    fgets(line, sizeof(line), stdin);
    int m = 0;
    token = strtok(line + 1, ",]");
    while (token != NULL) {
        wage[m++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    int k;
    scanf("%d", &k);
    
    double result = solution(quality, wage, n, k);
    printf("%f\n", result);
    
    return 0;
}