from atcoder.segtree import SegTree

N,M,A = map(int,input().split())
ST = SegTree(max, 0, [0] * (N+1))
LRP = [list(map(int,input().split())) for _ in range(M)]
LRP.sort(key = lambda x:x[1])
ans = 0
for l,r,p in LRP:
    if l == 1:
        x = p - A
        if r == N:
            x += A
        if x > ST.get(r):
            ST.set(r,x)
        ans = max(ans,x)
    else:
        x = ST.prod(0,l-2)
        y = ST.get(l-1) + A
        if y > 1:
            x = max(x,y)
        x += p - 2 * A
        if r == N:
            x += A
        if x > ST.get(r):
            ST.set(r,x)
        ans = max(ans,x)
print(ans)