import java.util.*; 
 
public class Knapsack { 
    public static double greedyKnapSack(ItemValue[] arr, int capacity) { 
        Arrays.sort(arr, new Comparator<ItemValue>() { 
            public int compare(ItemValue item1, ItemValue item2) { 
                double cpr1 = (double) item1.profit / item1.weight; 
                double cpr2 = (double) item2.profit / item2.weight; 
 
                if (cpr1 < cpr2) 
                    return 1; 
                else 
                    return -1; 
 
            } 
        }); 
 
        double total = 0; 
 
        for (ItemValue i : arr) { 
            if ((capacity - i.weight) >= 0) { 
                capacity -= i.weight; 
                total += i.profit; 
            } else { 
                double fract = (double) capacity / (double) i.weight; 
                total += fract * (i.profit); 
                capacity = 0; 
                break; 
            } 
        } 
        return total; 
    } 
 
    public static void main(String[] args) { 
        Scanner sc = new Scanner(System.in); 
        System.out.println("Enter the number of items: "); 
        int n = sc.nextInt(); 
        ItemValue[] arr = new ItemValue[n]; 
        System.out.println("Enter weight, profit of each item: "); 
        for (int i = 0; i < n; i++) { 
            arr[i] = new ItemValue(sc.nextInt(), sc.nextInt()); 
        } 
        System.out.println("Enter capacity :"); 
        int m = sc.nextInt(); 
 
        double pro = greedyKnapSack(arr, m); 
        System.out.println(pro); 
    } 
 
} 
 
class ItemValue { 
    public int weight; 
    public int profit; 
 
    public ItemValue(int weight, int profit) { 
        this.weight = weight; 
        this.profit = profit; 
    } 
 
}