MOD = 998244353
K = int(input())
X = [list(map(int,input().split())) for _ in range(K)]
N = 0
for i in range(K):
    N += X[i][0]*X[i][1]
A = [1]*(N+1)
for i in range(2,N+1):
    A[i] = (A[i-1]*i)%MOD
B = [1]*(N+1)
B[N] = pow(A[N],MOD-2,MOD)
for i in range(N-1,1,-1):
    B[i] = (B[i+1]*(i+1))%MOD
deno = 1
for i in range(K):
    deno = (deno*pow(A[X[i][0]],X[i][1],MOD)*A[X[i][1]])%MOD
ans = (A[N]*pow(deno,MOD-2,MOD))%MOD
print(ans)