N = int(input())
ANS = 0
for i in range(N):
  C, D = map(int, input().split())
  if C % 2 == 1:
    COST = (C // 2 + 1) * D
  else:
    COST = C // 2 * D
  ANS += COST
  ANS %= (10 ** 9 + 7)
print(ANS)