MOD = 998244353
K = int(input())
X = [list(map(int,input().split())) for _ in range(K)]
L = [X[i][0] for i in range(K)]
M = [X[i][1] for i in range(K)]
N = 0
for i in range(K):
    N += L[i]*M[i]
nume = 1
for i in range(2,N+1):
    nume = (nume*i)%MOD
deno = 1
j = 0
a = 1
for i in range(1,L[K-1]+1):
    a = a*i
    if i==L[j]:
        deno = (deno*pow(a,M[j],MOD))%MOD
        j += 1
M = sorted(M)
C = {}
for i in range(K):
    if M[i] not in C:
        C[M[i]] = 0
    C[M[i]] += 1
C = sorted(list(C.items()),key=lambda x:x[0])
j = 0
b = 1
for i in range(1,M[K-1]+1):
    b = b*i
    if i==C[j][0]:
        deno = (deno*pow(b,C[j][1],MOD))%MOD
        j += 1
ans = (nume*pow(deno,MOD-2,MOD))%MOD
print(ans)