#include <iostream>
#include <stdio.h>
#include <algorithm>
using namespace std;
struct node {
	int x, y;
	double price;
}node;
bool cmp(struct node x, struct node y) {
	return x.price > y.price;
}
int main() {
	int n, m; cin >> n >> m;
	struct node* num = new struct node[n];
	for (int i = 0; i < n; i++) {
		cin >> num[i].x >> num[i].y;
		num[i].price = (num[i].y * 1.0) / num[i].x;
	}
	sort(num, num + n, cmp);
	int i = 0;
	double sum = 0;
	while (m > 0) {
		if (m <= num[i].x) {
			sum += m * num[i].price;
			m = 0;
		}
		else{
			sum += num[i].x * num[i].price;
			m -= num[i].x;
		}
		i++;
	}
	printf("%.2f", sum);
}