#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005

int main() {
    ll n, m, A;
    cin >> n >> m >> A;
    vector<pair<P,ll>> v;
    rep(i,m){
        pair<P,ll> p;
        cin >> p.first.first >> p.first.second >> p.second;
        v.push_back(p);
    }
    sort(v.begin(), v.end());

    ll dp[n+1] = {};
    srep(i,1,n) dp[i] = -A;

    rep(i,m){
        int l = v[i].first.first;
        int r = v[i].first.second;
        ll p = v[i].second;
        if(r == n){
            dp[r] = max(dp[r], dp[l-1] + p);
        }else{
            dp[r] = max(dp[r], dp[l-1] + p - A);
        }
    }

    ll ans = 0;
    rep(i,n+1) ans = max(ans, dp[i]);

    cout << ans << endl;
    return 0;
}