H, W, K = gets.split.map(&:to_i)
MOD = 998_244_353

def f(h)
  return 0 if h <= 0

  h * (1 + h) / 2
end

ans = 0

K.times do
  x, y, v = gets.split.map(&:to_i)

  cnt = 0
  cnt += f(x) - f(x - y)
  cnt += f(x) - f(x - (W - y + 1))
  cnt -= x

  ans += v * cnt
  ans %= MOD
end

puts ans