n = int(input())
mod = 998244353

TV = [list(map(int,input().split())) for i in range(n)]
P = [1]
Q = [TV[0][0]]
s = TV[0][0]
for t,v in TV[1:]:
    P.append(Q[-1]+1)
    Q.append(Q[-1]+t)
    P[-1] %= mod
    Q[-1] %= mod
    s += t
    s %= mod
ans = 0
def f(x):
    return x*(x+1)*(x+2)*(4*s+3-3*x)%mod
inv = pow(24,mod-2,mod)
for i in range(n):
    v,p,q = TV[i][1],P[i],Q[i]
    ans += v*(f(q)-f(p-1))
    ans %= mod
print((ans*inv)%mod)