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

def sub(a, b):
    return a[0] - b[0], a[1] - b[1]
def det(a, b):
    return a[0] * b[1] - a[1] * b[0]

mod = 998244353
n = ni()
p = [na() for i in range(n)]

ans = 0
for i in range(n-2):
    ans -= det(sub(p[i+2], p[0]), sub(p[i+1], p[0]))

print(ans * pow(2, mod-2, mod) % mod)