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=int(input())
list1=[]
list2=[]
for i in range(n):
    ai,bi=map(int,input().split())
    list1.append((ai,bi,i+1))
list1.sort(key=lambda k:(k[1],k[2]))
for j in range(n-1):
    if list1[j][2]>list1[j+1][2]:
        list2.append(j+1)
list2.append(n)
a=0
if list2==[n]:
    for c in range(n):
        a=a+list1[0][1]*list1[c][0]
    print(a)
else:
    for d in range(list2[0]):
        a=a+list1[0][1]*list1[d][0]
    for m in range(1,len(list2)):
        for s in range(list2[m-1],list2[m]):
            a=a+list1[list2[m-1]][1]*list1[s][0]
    print(a)