#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,ll> P;
#define yn {puts("Yes");}else{puts("No");}
#define MAX_N 200005
vector<P> G[MAX_N];
int main() {
    ll n, m, A;
    cin >> n >> m >> A;
    vector<pair<P,ll>> v;
    rep(i,m){
        int l, r, p;
        cin >> l >> r >> p;
        G[l].push_back(P(r,p));
    }
    rep(i,MAX_N) sort(G[i].begin(), G[i].end());

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

    srep(j,1,n+1){
        if(j > 1) dp[j] = max(dp[j-1], dp[j]);
        rep(i,G[j].size()){
            int l = j;
            int r = G[j][i].first;
            ll p = G[j][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;
}