import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

s=0
k=II()
lm=LLI(k)
fac={}
s=0
for l,m in lm:
    fac[l]=fac[m]=0
    s+=l*m
fac[s]=0

f=1
for i in range(1,s+1):
    f=f*i%md
    if i in fac:fac[i]=f

den=1
for l,m in lm:
    den*=pow(fac[l],m,md)*fac[m]%md
    den%=md

ans=fac[s]*pow(den,md-2,md)%md
print(ans)