MOD = 998244353

def inverse(n, d):
    return n * pow(d, -1, MOD) % MOD

half = inverse(1, 2)

def area(x1, y1, x2, y2, x3, y3):
    return ((x1-x3)*(y2-y3)-(x2-x3)*(y1-y3))%MOD*half%MOD

N = int(input())
XY = [list(map(int, input().split())) for _ in range(N)]

ans = 0
for i in range(1, N-1):
    ans += area(*XY[0], *XY[i], *XY[i+1])
    ans %= MOD

print(ans)