INF = 10 ** 9
import sys
sys.setrecursionlimit(100000000)
dy = (-1,0,1,0)
dx = (0,1,0,-1)
from  collections import deque

def main():
    n,m,a = list(map(int,input().split()))
    kukann = [[] for i in range(n + 1)]
    for _ in range(m):
        l,r,p = map(int,input().split())
        l -= 1
        kukann[r].append((l,p))
    
    dp = [-a] * (n + 1)
    dp[0] = 0
    dp1 = [-a] * (n + 1)
    dp1[0] = 0
    for i in range(1,n):
        for l,p in kukann[i]:
                dp[i] = max(dp[i],dp[l] + p - a,dp1[l - 1] + p - 2 * a)

        dp1[i] = max(dp1[i - 1],dp[i])
    
    for l,p in kukann[n]:
        if l > 0:
            dp[n] = max(dp[n],dp[l] + p,dp1[l - 1] + p - a)
        else:
            dp[n] = max(dp[n],dp[0] + p)
    dp1[n] = max(dp1[n - 1],dp[n])

    print(max(dp1[-1],0))

if __name__ == '__main__':
    main()