N,M,A = map(int,input().split())

G = [[] for _ in range(N + 1)]
for _ in range(M):
    l,r,p = map(int,input().split())
    G[r].append((l,p))

dp = [0] * (N + 1)
_max = 0
index = 0
for i in range(1,N + 1):
    dp[i] = _max - A
    for l,p in G[i]:
        dp[i] = max(dp[i],dp[l-1] + p - A)
    if dp[i] > _max:
        _max = dp[i]
        index = i
dp[N] += A
print(max(dp))