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.
'''
3 3 -9
3 2 -12
3 4
3 1 -3

First shitty method: 9 + 6 + 12 + 3 (This just got the required num per step)

Second method: 9 + 12 + 3 = 24

Third: 9 + 18


'''

n = int(input())

ar = []
for _ in range(n):
    a = list(map(int,input().split()))
    ar.append(a)
count = 0
store = 0
for x in range(len(ar)):
    
    try:
        if store > 0:
            store = 0
        elif store == 0 and ar[x][1] > ar[x+1][1]:
            
            count += ar[x][0] * ar[x][1]
        else:
            count += (ar[x][0] + ar[x+1][0]) * ar[x][1]
            store = (ar[x][0] + ar[x+1][0])
    except:
        
        count += ar[x][0] * ar[x][1]
        
print(count)
    
