#include <stdio.h>
#include <string.h>
#include <string>
#include <vector>
#include <sstream>
#include <algorithm>
#include <iostream>
#include <cmath>
#include <queue>
using namespace std;

#define FOR(i,n) for (int i = 0; i < n; i++)
#define abs(x) ((x)<0?(-(x)):(x))
#define REP(i,v) for (unsigned i = 0; i < v.size(); i++)
#define RL(i,v) for (unsigned i = 0; i < v.length(); i++)
typedef long long ll;

const int MAX_N = 102;
const int MAX_P = 100100;

struct Item {
	int price, quantity;
	bool operator < (const Item& r) const {
		return price != r.price ? price > r.price : quantity > r.quantity;
	}
};

int n, space;
int a[MAX_N][2];
deque < Item > q;

void solve(void)
{
	FILE* f = fopen("summer.in", "rt");
	FILE* fo = fopen("summer.out", "wt");

	fscanf(f, "%d %d", &n, &space);
	for (int i = 0; i < n; i++)
		fscanf(f, "%d %d", &a[i][0], &a[i][1]);

	int ans = 0;
	for (int i = 0; i < n; i++)
	{
		int rem = a[i][0], price = a[i][1];
		while (rem > 0 && !q.empty() && q.front().price < price)
		{
			Item cur = q.front(); q.pop_front();
			if (cur.quantity <= rem)
			{
				ans += cur.quantity * cur.price;
				rem -= cur.quantity; space += cur.quantity;
			}
			else
			{
				ans += rem * cur.price;
				cur.quantity -= rem; space += rem; rem = 0;
				q.push_front(cur);
			}
		}
		ans += rem * price;
		while (!q.empty() && q.back().price >= price)
		{
			Item cur = q.back(); q.pop_back();
			space += cur.quantity;
		}
		if (space > 0)
		{
			Item add;
			add.price = price;
			add.quantity = space;
			q.push_back(add); space = 0;
		}
	}
	fprintf(fo, "%d\n", ans);

	fclose(f);
	fclose(fo);
}


int main(void)
{
	solve();
	return 0;
}