H, W, K = map(int, input().split())
mod = 998244353
total = 0

for _ in range(K):
    x, y, v = map(int, input().split())
    s = x + y
    t = x - y
    max_i = min(x, H, s - 1)
    if max_i < 1:
        continue
    
    # Region 1
    a = min(t, s - W, max_i)
    sum_r1 = a * W if a >= 1 else 0
    
    # Region 2
    l2 = max(s - W + 1, 1)
    b = min(t, s - 1, max_i)
    sum_r2 = 0
    if l2 <= b:
        cnt = b - l2 + 1
        sum_s = s * cnt
        sum_i = (b * (b + 1) // 2) - ((l2 - 1) * l2 // 2)
        sum_r2 = sum_s - sum_i
    
    # Region 3
    c = min(s - W, max_i)
    start3 = t + 1
    start3 = max(start3, 1)
    sum_r3 = 0
    if start3 <= c:
        cnt = c - start3 + 1
        const = W + t + 1
        sum_total_const = const * cnt
        sum_i = (c * (c + 1) // 2) - ((start3 - 1) * start3 // 2)
        sum_r3 = sum_total_const - sum_i
    
    # Region 4
    l4 = max(t + 1, s - W + 1)
    l4 = max(l4, 1)
    d = min(max_i, s - 1)
    sum_r4 = 0
    if l4 <= d:
        cnt = d - l4 + 1
        const = s + t + 1
        sum_const = const * cnt
        sum_i_part = (d * (d + 1) // 2) - ((l4 - 1) * l4 // 2)
        sum_i = 2 * sum_i_part
        sum_r4 = sum_const - sum_i
    
    sum_total = sum_r1 + sum_r2 + sum_r3 + sum_r4
    contribution = (sum_total % mod) * (v % mod)
    total = (total + contribution) % mod

print(total % mod)