import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
inf = 10**16
md = 998244353
# md = 10**9+7

inv = pow(24, md-2, md)

def coef(s, t):
    res = (s-t-1)*(3*(pow(s, 3, md)+pow(s, 2, md)*(t+3)+s*(pow(t, 2, md)+4*t+2)+t*(pow(t, 2, md)+5*t+6))-4*tn*(
            pow(s, 2, md)+s*(t+4)+pow(t, 2, md)+5*t+6))*inv
    return res%md

n = II()
tt, vv = [], []
for _ in range(n):
    t, v = LI()
    tt.append(t%md)
    vv.append(v)

l = r = 0
tn = sum(tt)%md
ans = 0
for t, v in zip(tt, vv):
    r = l+t-1
    ans += coef(l, r)*v
    ans %= md
    l = r+1

print(ans)