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.
import copy
Totalday = int(input())
Condit_list = []
quitList = []
Money = 0
for day in range(Totalday):
    Input = input().split(" ")
    Condit_list.append([day+1,int(Input[0]),int(Input[1])])
Condit_list.sort(key=lambda x:x[2])
Change_condit_list = copy.deepcopy(Condit_list)
for Elem in Condit_list:
    Change_condit_list.remove(Elem)
    for Elem2 in Change_condit_list:
            if Elem[0] < Elem2[0]:
                Elem[1] += Elem2[1]
                quitList.append(Elem2)
for i in quitList:
    Condit_list.remove(i)
for Get in Condit_list:
    Money += Get[1]*Get[2]
print(Money)