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())
s=0
a=[]
b=[]
for i in range(0,n):
    x=input()
    xx=x.split( )
    a.append(int(xx[0]))
    b.append(int(xx[1]))
if len(a)==1:
    print(a[0]*b[0])
else:
    i=0
    while i!=n:
        if i!=n-1:
            h=i
            s+=(b[i]*a[i])
            q=0
            while b[i]<b[h+1]:
                s+=(b[i]*a[h+1])
                h+=1
                q+=1
                if h==n-1:
                    break
            if q!=0:
                i=h
            else:
                i+=1
        else:
            if i!=h:
                s+=(b[i]*a[i])
            i+=1
    print(s)
        
