def rectangle(len):
    return 0 if len < 0 else ((len)*(len+1)//2)


def inverted(W, I, J, V):
    cnt = (I+1)*(I+1)-rectangle(I-J)-rectangle(I+J+1-W)
    return V * cnt % 998244353


def main():
    H, W, K = map(int, input().split())
    assert(1 <= H and H <= 100000)
    assert(1 <= W and W <= 100000)
    assert(0 <= K and K <= min(H*W, 200000))

    XYVs = [None for _ in range(K)]
    for i in range(K):
        X, Y, V = map(int, input().split())
        assert(1 <= X and X <= H)
        assert(1 <= Y and Y <= W)
        assert(0 <= V and V <= 1000000000)
        X -= 1
        Y -= 1
        XYVs[i] = (X, Y, V)

    ans = 0
    for x, y, v in XYVs:
        ans += inverted(W, x, y, v)
    print(ans % 998244353)


if __name__ == '__main__':
    main()