import sys
input = sys.stdin.readline

def f(a, b):
    return (3*a**4-2*a**3*(2*S+3)-3*a**2+a*(4*S+6)-b*(b**2+3*b+2)*(3*b-4*S-3))//24

N = int(input())
S = 0
TV = []

for _ in range(N):
    T, V = map(int, input().split())
    S += T
    TV.append((T, V))

ans = 0
acc = 1
MOD = 998244353

for T, V in TV:
    ans += f(acc, acc+T-1)*V
    ans %= MOD
    acc += T
    acc %= MOD

print(ans)