mod = 998244353
n = int(input())
x = [0] * n
y = [0] * n
for i in range(n):
	x[i], y[i] = map(int,input().split())

ans = 0
for i in range(n-2):
	ax = x[i+1] - x[0]
	bx = y[i+1] - y[0]
	ay = x[i+2] - x[0]
	by = y[i+2] - y[0]
	ans += ax * by - ay * bx

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