n = int(raw_input())
ans = 0
#mod = 10**9 + 7
mod = int(1e9 + 7)

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

print(ans)