P = 10**9 + 7

n = int(input())
rs: list[tuple[int, int]] = []
for _ in range(n):
    t, x = map(int, input().split())
    if t == 1:
        rs.append((x - 1, 1))
    else:
        rs.append((x, 0))
rs.sort()

pd = [1]
for i, (r, f) in enumerate(rs):
    print(i, r, f)
    dp = [0] * (i + 2)
    for j in range(i + 1):
        num = r - j
        if f == 1:
            dp[j + 1] -= pd[j] * num % P
            dp[j] += pd[j]
        else:
            dp[j + 1] += pd[j] * num % P
    pd = [e % P for e in dp]
ans = 0
fac = 1
for j in reversed(range(n + 1)):
    ans += pd[j] * fac % P
    fac = fac * (n - j + 1) % P
print(ans % P)