import sys

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 19
MOD = 10 ** 9 + 7
EPS = 10 ** -10

N, M, K = MAP()

RL = [[] for i in range(N+1)]
for i in range(M):
    l, r, p = MAP()
    l -= 1
    RL[r].append((l, p))

dp0 = [0] * (N+1)
dp1 = [0] * (N+1)
for r in range(1, N+1):
    dp0[r] = max(dp0[r-1], dp1[r-1])
    for l, p in RL[r]:
        if r == N:
            dp1[r] = max(dp1[r], dp0[l] + p-K)
            dp1[r] = max(dp1[r], dp1[l] + p)
        else:
            dp1[r] = max(dp1[r], dp0[l] + p-K*2)
            dp1[r] = max(dp1[r], dp1[l] + p-K)
ans = max(dp0[N], dp1[N])
print(ans)