/* -*- coding: utf-8 -*-
 *
 * 2229.cc:  No.2229 Treasure Searching Rod (Hard) - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_K = 200000;
const int MOD = 998244353;

/* typedef */

typedef long long ll;

/* global variables */

int xs[MAX_K], ys[MAX_K], vs[MAX_K];

/* subroutines */

inline ll sigma(int n) { return (ll)n * (n + 1) / 2; }

/* main */

int main() {
  int h, w, k;
  scanf("%d%d%d", &h, &w, &k);
  for (int i = 0; i < k; i++)
    scanf("%d%d%d", xs + i, ys + i, vs + i);

  int sum = 0;
  for (int i = 0; i < k; i++) {
    int dx = xs[i];
    int y0 = max(0, dx - ys[i]), y1 = max(0, ys[i] + dx - 1 - w);
    ll s0 = sigma(dx) - sigma(y0), s1 = sigma(dx) - sigma(y1);
    ll s = s0 + s1 - dx;
    //printf("x=%d,y=%d -> s=%lld\n", xs[i], ys[i], s);
    sum = (sum + s % MOD * vs[i] % MOD) % MOD;
  }

  printf("%d\n", sum);
  return 0;
}