#include<bits/stdc++.h>
using namespace std;
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define debug(v) cout<<#v<<":";for(auto x:v){cout<<x<<' ';}cout<<endl;
#define INF 1000000000
#define mod 1000000007
using ll=long long;
const ll LINF=1001002003004005006ll;
int dx[]={1,0,-1,0};
int dy[]={0,1,0,-1};
// ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    ll n,m,a;cin>>n>>m>>a;
    ll dp[n+1]={};
    for(int i=1;i<=n;i++)dp[i]=-a;

    vector<vector<pair<ll,ll>>> g(n+1);
    rep(i,m){
        ll l,r,p;cin>>l>>r>>p;l--;
        g[r].push_back(make_pair(l,p));
    }
    ll mx=dp[0];
    for(int i=1;i<=n;i++){
        chmax(dp[i],mx-(i==n?0:a));
        for(auto p:g[i]){
            chmax(dp[i],dp[p.first]+p.second-(i==n?0:a));
        }
        chmax(mx,dp[i]);
    }
    ll ans=0;
    rep(i,n+1)chmax(ans,dp[i]);
    cout<<ans<<endl;
    return 0;
}