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())
li = []
cst = []
for i in range(n):
    a,b = map(int,input().split())
    li.append(a)
    cst.append(b)
min_cst = min(cst)
res = 0
st = False
tmp = 0
chk = 0
for i in range(n):
    if i == 0:
        tmp = cst[i]
        res += li[i]*cst[i]
        continue
    if tmp < cst[i]:
        st = True
        chk += li[i]
    else:
        if st == True:
            res += chk * tmp
            chk = 0
            tmp = li[i]
            st = True
        else:
            res += li[i] * cst[i]
            tmp = cst[i]
            chk = 0
if chk > 0:
    res += chk * tmp
print(res)

