h, w, k = map(int, input().split())
mod = 998244353
ans = 0
inv2 = pow(2, mod - 2, mod)
for _ in range(k):
    x, y, v = map(int, input().split())
    cnt = pow(x, 2, mod)
    if y < x:
        d = x - y
        cnt -= d * (d + 1) % mod * inv2 % mod
        cnt %= mod
    if (w - y) < x - 1:
        d = x - (w - y) - 1
        cnt -= d * (d + 1) % mod * inv2 % mod
        cnt %= mod
    ans += v * cnt % mod
    ans %= mod
print(ans)