N,M,A = map(int,input().split())
B = sorted([list(map(int,input().split())) for _ in range(M)],key=lambda x:x[0])
B = sorted(B,key=lambda x:x[1])
dp = [[0 for _ in range(2)] for _ in range(N+1)]
ind = 0
dp[1][1] = -A
if B[0][1]==1:
    dp[1][1] = B[0][2]-A
    ind = 1
dpmax = max(dp[1][0],dp[1][1])
for i in range(2,N+1):
    dp[i][0] = dpmax
    if ind<M and B[ind][1]>i:
        dp[i][1] = dpmax-A
    elif ind<M and B[ind][1]==i:
        while ind<M and B[ind][1]==i:
            if B[ind][1]<N:
                dp[i][1] = max(dp[i][1], -A + B[ind][2] + max(dp[B[ind][0] - 1][1], dp[B[ind][0] - 1][0] - (A if B[ind][0] - 1 > 0 else 0)))
            else:
                dp[i][1] = max(dp[i][1], B[ind][2] + max(dp[B[ind][0] - 1][1], dp[B[ind][0] - 1][0] - (A if B[ind][0] - 1 > 0 else 0)))
            ind += 1
    else:
        dp[i][1] = dpmax-A
    dpmax = max(dpmax,dp[i][0],dp[i][1])
print(max(dp[N]))