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.
a=int(input())
z=a
x=0
y=[]
k=3
j=0
h=0
l=1

while 1<=z<=100000:
    b=input().split()
    y.extend(b)
    z=z-1

h=int(y[j])
if a==1:
    x=int(y[0])*int(y[1])
while k<=((a*2)-1):
    if int(y[l])<=int(y[k]):
        j=j+2
        h=h+int(y[j])

        
        if k==(a*2-1):
            x=x+(int(y[l])*h)
            break
        k=k+2
        
    elif int(y[l])>int(y[k]):
        
        x=x+(int(y[l])*h)
        l=k
        
        j=j+2
        h=int(y[j])
        if k==(a*2-1):
            
            x=x+(int(y[l])*h)
            break
        k=k+2

    

    
print(x)
