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.
dias = int(input())
kilos= []
precios = []
suma = 0
total = 0
for i in range(dias):
    datos = list(str(input()).split())
    datos[0] = int(datos[0])
    datos[1] = int(datos[1])
    kilos.append(datos[0])
    precios.append(datos[1])

for i in range(len(precios)):
    cantidad = precios[i]
    contador = i
    for j in range(i,len(precios)):
        if precios[j]<cantidad:
            suma = 0
            for h in range(i,j):
                suma += kilos[h]
            total += suma*cantidad
            i = j
            break
        if j+1 == len(precios):
            suma = 0
            for k in range(i,len(precios)):
                suma += kilos[k]
            total += suma*precios[i]
            break
    if i == contador:
        break

print(total)
			 						 	     			 				 				