import sys
input = sys.stdin.readline

class SegmentTree:
    def __init__(self, N, func, ele):
        n_ = 1
        
        while n_<N:
            n_ *= 2
            
        self.n = n_
        self.func = func
        self.ele = ele
        self.arr = [self.ele]*(2*self.n-1)
    
    def update(self, k, a):
        k += self.n-1
        self.arr[k] = a
        
        while k>0:
            k = (k-1)//2
            self.arr[k] = self.func(self.arr[2*k+1], self.arr[2*k+2])
        
    def query(self, l, r):
        L, R = l+self.n, r+self.n
        res = self.ele
        
        while L<R:
            if R&1:
                R -= 1
                res = self.func(res, self.arr[R-1])
            
            if L&1:
                res = self.func(res, self.arr[L-1])
                L += 1
            
            L >>= 1
            R >>= 1
            
        return res

N, M, A = map(int, input().split())
lrp = [tuple(map(int, input().split())) for _ in range(M)]
lrp.sort(key=lambda k: k[0])
dp = [-10**18]*N
st = SegmentTree(N, max, -10**18)

ans = 0

for li, ri, pi in lrp:
    li -= 1
    ri -= 1
    
    if li==0:
        dp[ri] = max(dp[ri], pi-A)
    else:
        dp[ri] = max(dp[ri], pi-2*A)
        dp[ri] = max(dp[ri], st.query(0, li)+pi-2*A)
        dp[ri] = max(dp[ri], dp[li-1]+pi-A)
    
    st.update(ri, dp[ri])
    
    if ri==N-1:
        ans = max(ans, dp[ri]+A)
    else:
        ans = max(ans, dp[ri])
    
print(ans)