import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N = I()
mod = 998244353

TV = []
M = 0  # Aの項数
for _ in range(N):
    T,V = MI()
    M += T
    TV.append((T,V))


def sum_power(n,i):  # 1^i+2^i+…+n^i
    if i == 1:
        res = n*(n+1)//2
    elif i == 2:
        res = n*(n+1)*(2*n+1)//6
    else:
        res = n**2*(n+1)**2//4
    return res % mod


def f(n):
    res = (M+1)*((sum_power(n,1)+sum_power(n,2))//2)-(sum_power(n,2)+sum_power(n,3))//2
    return res % mod


l = 0
ans = 0
for T,V in TV:
    r = l+T
    ans += (f(r)-f(l))*V
    ans %= mod
    l = r

print(ans)