def main():
    import sys
    input = sys.stdin.buffer.readline

    N, M, x = map(int, input().split())
    info = [None] * M
    for i in range(M):
        info[i] = tuple(map(int, input().split()))
    info.sort(key=lambda e: e[0])
    info.sort(key=lambda e: e[1])

    dp = [-x] * (N+2)
    dp[1] = 0
    for l, r, p in info:
        flg = int(r!=N)
        dp[r+1] = max(dp[r+1], dp[l] + p - x * flg)
    print(max(dp))


if __name__ == '__main__':
    main()