import sys
m = 10**9+7
n = int(input())
l = [list(map(int, s.split())) for s in sys.stdin]
l = sorted((x-t, t) for t, x in l)
if sum(t for x, t in l) > len(l)//2:
    l = [(n-x, 1-t) for x, t in reversed(l)]
c = [1]+[0]*n
d = 1
for i, (x, t) in enumerate(l):
    d += t
    for j in range(d-1, -1, -1):
        c[j] = (c[j-1]*j - c[j]*(x-i+j) if t else c[j]*(x-i+j)) % m
print(sum(c)%m)