n = int(raw_input())
ans = 0
mod = 1e9 + 7

for i in range(1, n + 1):
	c, d = map(int, raw_input().split())
	if c % 2 == 0:
		ans += (c / 2) * d
	else:
		ans += (c / 2 + 1) * d
	ans %= mod

print(int(ans))