N,M,A = map(int,input().split())
lsscore = [[] for i in range(N+1)]
for i in range(M):
    l,r,p = map(int,input().split())
    lsscore[r].append((l,p))

dp = [float('INF')]*(N+1)
dp[0] = 0
mm = 0
for i in range(1,N):
    mm = max(dp[i-1],mm)
    s = mm-A
    for j,p in lsscore[i]:
        s = max(dp[j-1]+p-A,s)
    dp[i] = s
mm = max(dp[N-1],mm)
s = mm
for j,p in lsscore[N]:
    s = max(dp[j-1]+p,s)
dp[N] = s
print(max(dp))