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.
n_days = input()
meat_amount = []
meat_price = []
total_meat = 0


for i in range(n_days):
    tuple_input = raw_input().split(' ')
    meat_amount.append(int(tuple_input[0]))
    total_meat += int(tuple_input[0])
    meat_price.append(int(tuple_input[1]))

best_value = total_meat * meat_price[0]
total_meat -= meat_amount[0]
partial_sum = meat_amount[0] * meat_price[0]

for i in range(1, n_days):
    partial_sum += meat_amount[i] * meat_price[i]
    total_meat -= meat_amount[i]
    temp = partial_sum + meat_price[i] * total_meat
    if temp < best_value:
        best_value = temp

print best_value