h,w,k = map(int,input().split())
ans = 0
mod =998244353
now = 1
xx = [0]
for i in range(2*10**5):
  xx.append(xx[-1] + now)
  now += 2
  now %= mod
for i in range(k):
  x,y,v = map(int,input().split())
  cnt = xx[x]
  lcnt = max(0,x-y)
  rcnt = max(0, x-(w-y+1))
  cnt -= lcnt*(lcnt+1)//2 + rcnt*(rcnt+1)//2
  cnt %= mod
  ans += v * cnt
  ans %= mod

print(ans)