MOD = 10**9 + 7

n = int(input())
ans = 0

for _ in range(n):
    c, d = map(int, input().split())
    max_per = (c + 1) // 2
    term = (max_per % MOD) * (d % MOD) % MOD
    ans = (ans + term) % MOD

print(ans)