MOD = 998244353
"""
n = 6
A = [3, 3, 2, 1, 1, 1]
ans = 0
for i, a in enumerate(A):
    ans += a * (n - i) * (i + 1) * (i + 2) // 2
print(ans)
"""

n = int(input())
tv = [list(map(int, input().split())) for _ in range(n)]
n = sum(t for t, _ in tv) % MOD
inv2 = pow(2, MOD - 2, MOD)
inv6 = pow(6, MOD - 2, MOD)

def f(x):
    if x == -1:
        return 0
    ret = 0
    
    three = x * (x + 1) * inv2
    three = pow(three, 2, MOD)
    ret -= three
    ret %= MOD
    
    two = x * (x + 1) * (2 * x + 1) * inv6
    ret += (n - 3) * two
    ret %= MOD
    
    one = x * (x + 1) * inv2
    ret += (3 * n - 2) * one
    ret %= MOD
    
    ret += 2 * n * (x + 1)
    
    ret *= inv2
    return ret % MOD
    
    for i in range(x + 1):
        ret += (n - i) * (i + 1) * (i + 2) // 2
    return ret
    
    
ans = 0
l = 0
for t, v in tv:
    ans += v * (f(l + t - 1) - f(l - 1))
    ans %= MOD
    l += t
print(ans)