MOD = 998244353

half = pow(2, -1, MOD)
def rangeSUM(l, r, c):
    return (l+r)%MOD*c%MOD*half%MOD

def func(h, w):
    l, r = max(h-w+1, 1), h
    return rangeSUM(l, r, r-l+1)

H, W, K = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(K)]

ans = 0
for h, w, v in A:
    ans += (func(h, w)+func(h, W-w+1)-h)*v%MOD
    ans %= MOD

print(ans)