MOD = 998244353
n = int(input())
t = [0] * n
v = [0] * n
for i in range(n):
    t[i], v[i] = map(int, input().split())
l = sum(t)
v24 = pow(24, MOD - 2, MOD)

def f(k):
    return k * (k + 1) * (k + 2) * (4 * l - 3 * k + 3) * v24 % MOD

ans = 0
p = 0
for i in range(n):
    ans += (f(p + t[i]) - f(p)) * v[i]
    p += t[i]
print(ans % MOD)