n = int(input())

res = 0
mod = 10**9 + 7
for _ in range(n):
    c, d = [int(x) for x in input().split()]
    if c % 2 == 0:
        can = c // 2
    else:
        can = c // 2 + 1
    res += (can % mod * d % mod) % mod
    res %= mod

print(res)