import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
sys.setrecursionlimit(10**7)
yes = lambda :print("yes");Yes = lambda :print("Yes")
no = lambda :print("no");No = lambda :print("No")
#######################################################################


n = ni()
s = 0
ans = 0
m = 998244353
m24 = pow(24,m-2,m)
tv = [na() for i in range(n)]
N=0
for i in range(n):
    N+=tv[i][0]
def g(x,y):
    return x*y%m
def f(x):
    return g(g(g(g(x,x-1),x+1),4*N-3*x+6),m24)

for i in range(n):
    #print((f(s+tv[i][0]+1)-f(s))%m)
    ans+=g(tv[i][1],(f(s+tv[i][0]+1)-f(s+1))%m)%m
    ans%=m
    s+=tv[i][0]
    s%=m
    #print(s)

print(ans)