import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

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

dp0 = [0] * (N + 1)
dp1 = [0] * (N + 1)

tmp = 0
for r in range(N+1):
    # 線を引く
    get = 0
    for l, x in LX[r]:
        get = max(get, dp0[l - 1] + x)
        if l == 1:
            get = max(get, dp1[l - 1] + x)
        else:
            get = max(get, dp1[l - 1] + x - A)
    if r < N:
        dp0[r] = get - A
    else:
        dp0[r] = get

    # 線を引かない
    tmp = max(tmp, dp0[r-1], dp1[r-1])
    dp1[r] = tmp

print(max(dp0[N], dp1[N]))