3262.py

n = input()

cow_list = []
def eated_flower(list,time,cnt=0):
    num = 0
    for l in list:
        num += l[1 + cnt] * time
    return num

c2 = []
for i in range(n):
    c = raw_input().split(" ")
    c2.append( [int(c[0]),int(c[1])] )
for i in range(n):
    cow_list.append([float(c2[i][1]) / c2[i][0],c2[i][0],c2[i][1] ] )
cow_list.sort()
cow_list.reverse()
ans = 0
for i in range(len(cow_list)):
    ans += eated_flower(cow_list[i+1:len(cow_list)],cow_list[i][1] * 2,1)
            

print ans