Duff is addicted to meat! Malek wants to keep her happy for *n* days. In order to be happy in *i*-th day, she needs to eat exactly *a*<sub class="lower-index">*i*</sub> kilograms of meat.

There is a big shop uptown and Malek wants to buy meat for her from there. In *i*-th day, they sell meat for *p*<sub class="lower-index">*i*</sub> dollars per kilogram. Malek knows all numbers *a*<sub class="lower-index">1</sub>, ..., *a*<sub class="lower-index">*n*</sub> and *p*<sub class="lower-index">1</sub>, ..., *p*<sub class="lower-index">*n*</sub>. In each day, he can buy arbitrary amount of meat, also he can keep some meat he has for the future.

Malek is a little tired from cooking meat, so he asked for your help. Help him to minimize the total money he spends to keep Duff happy for *n* days.
The first line of input contains integer *n* (1 ≤ *n* ≤ 10<sup class="upper-index">5</sup>), the number of days.

In the next *n* lines, *i*-th line contains two integers *a*<sub class="lower-index">*i*</sub> and *p*<sub class="lower-index">*i*</sub> (1 ≤ *a*<sub class="lower-index">*i*</sub>, *p*<sub class="lower-index">*i*</sub> ≤ 100), the amount of meat Duff needs and the cost of meat in that day.
days = int(input())
i = 0
meat_needs = []
meat_prices = []
while i < days:
	meat, price = (int(x) for x in input().split())
	meat_needs.append(meat)
	meat_prices.append(price)
	i += 1
price_index = []
start = 0
end = days
while end > 0:
	min_price = min(meat_prices[start:end])
	min_pr_index = meat_prices.index(min_price)
	price_index.append([min_price, min_pr_index])
	end = min_pr_index
price_index.reverse()
live_cost = 0
j = 0
for price, index in price_index:
	while j < index + 1:
		live_cost += meat_needs[j]*price
		j += 1
	j = index + 1
price, index = price_index[-1]
j = index + 1
while j < days:
	live_cost += meat_needs[j]*price
	j += 1
print(live_cost)