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
A1 = [1]*(L[K-1]+1)
for i in range(2,L[K-1]+1):
    A1[i] = (A1[i-1]*i)%MOD
Mmax = max(M)
A2 = [1]*(Mmax+1)
for i in range(2,Mmax+1):
    A2[i] = (A2[i-1]*i)%MOD
deno = 1
for i in range(K):
    deno = (deno*pow(A1[L[i]],M[i],MOD)*A2[M[i]])%MOD
ans = (nume*pow(deno,MOD-2,MOD))%MOD
print(ans)