#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, ll> P;

int main()
{
    int n, m; ll a; cin>>n>>m>>a;
    ll dp[100010];
    fill(dp, dp+n+1, -a);
    dp[0]=0;
    vector<P> v[100010];
    for(int i=0; i<m; i++){
        int l, r; ll p; cin>>l>>r>>p;
        v[r].push_back({l, p});
    }
  ll ans=0;
  ll mx[100010];
  mx[0]=0;
    for(int i=1; i<=n; i++){
        for(auto p:v[i]){
            dp[i]=max({dp[i], dp[p.first-1]-a+p.second, mx[max(p.first-2, 0)]-2*a+p.second});
        }
        mx[i]=max(mx[i-1], dp[i]);
      ans=max(dp[i], ans);
    }
  ans=max(ans, dp[n]+a);
    cout<<ans<<endl;
    return 0;
}