__author__ = 'Zlobober'
n = int(raw_input())
A = []
P = []
for i in range(n):
    a, p = map(int, raw_input().split())
    A.append(a)
    P.append(p)
mn = 142
ans = 0
for i in range(n):
    mn = min(mn, P[i])
    ans += A[i] * mn
print ans