import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

N = int(input())
ans = 0
mod = 10 ** 9 + 7
for _ in range(N):
    c, d = map(int, input().split())
    c = (c + 1) // 2
    ans += c * d
    ans %= mod
print(ans)