import sys,random,bisect
from collections import deque,defaultdict
from heapq import heapify,heappop,heappush
from itertools import permutations
from math import gcd,log

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

mod = 998244353

H,W,K = mi()
tre = []
res = 0
for _ in range(K):
    x,y,v = mi()
    x,y = x-1,y-1


    """
    1 <= i <= H
    1 <= j <= W

    i+j <= x+y
    i-j <= x-y

    をみたすijの数え上げ

    for i in range(H):
        j_min = max(0,i-(x-y))
        j_max= min(W-1,x+y-i)
    """

    tmp = 0
    i_upper = min(x+1,H,W+x-y,x+y+1)
    if i_upper <= 0:
        continue
    
    tmp = i_upper

    c = x+y-(W-1)
    if 0 <= c <= i_upper:
        tmp += c * (W-1)
        tmp += (x+y) * (i_upper-c)
        tmp -= i_upper*(i_upper-1)//2 - c*(c-1)//2
    elif c < 0:
        tmp += (x+y) * i_upper
        tmp -= i_upper*(i_upper-1)//2
    else:
        tmp += i_upper * (W-1)


    if max(0,x-y) < i_upper:
        tmp += (x-y) * (i_upper-max(0,x-y))
        tmp -= i_upper*(i_upper-1)//2 - max(0,x-y)*(max(0,x-y)-1)//2
    res += v * tmp % mod

print(res % mod)