#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> P;

#define fi first
#define se second
#define repl(i,a,b) for(ll i=(ll)(a);i<(ll)(b);i++)
#define rep(i,n) repl(i,0,n)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define mmax(x,y) (x>y?x:y)
#define mmin(x,y) (x<y?x:y)
#define maxch(x,y) x=mmax(x,y)
#define minch(x,y) x=mmin(x,y)
#define uni(x) x.erase(unique(all(x)),x.end())
#define exist(x,y) (find(all(x),y)!=x.end())
#define bcnt __builtin_popcountll

#define INF 1e16
#define mod 1000000007

ll N,M,A;
vector<P> rs[100010];
ll dp[100010][2];

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin>>N>>M>>A;
  rep(i,M){
    ll a,b,c;
    cin>>a>>b>>c;
    a--;
    rs[b].push_back(P(a,c));
  }

  rep(i,N+1)dp[i][0]=dp[i][1]=-INF;

  dp[0][1]=0;
  repl(i,1,N+1){
    for(P r : rs[i]){
      if(i<N){
        maxch(dp[i][1],dp[r.fi][0]+r.se-2*A);
        maxch(dp[i][1],dp[r.fi][1]+r.se-A);
      }else{
        maxch(dp[i][1],dp[r.fi][0]+r.se-A);
        maxch(dp[i][1],dp[r.fi][1]+r.se);
      }
    }
    maxch(dp[i][0],dp[i-1][0]);
    maxch(dp[i][0],dp[i-1][1]);
  }
  cout<<max(dp[N][0],dp[N][1])<<endl;

  return 0;
}