# No.146 試験監督（1）
N = int(input())
C = []
D = []

for i in range(N):
    c, d = [int(j) for j in input().split()]
    C.append(c)
    D.append(d)

examinee = 0

for i in range(N):
    examinee += (C[i] // 2 if C[i] % 2 == 0 else C[i] //2 + 1) * D[i]

print(examinee % (10 ** 9 + 7))