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

#define int long long

vector<pair<int, int> > vec[100010];


signed main(){
    int n, m, a;
    cin >> n >> m >> a;


    for(int i = 0;i < m;i++){
        int l, r, p;
        cin >> l >> r >> p;
        l--;
        vec[l].push_back(make_pair(r, p));
    }

    int dp1[100010] = {};
    int d1tmp[100010] = {};
    int dp2[100010] = {};

    for(int i = 0;i < 100010;i++){
        dp1[i] = dp2[i] = -(1ll << 60);
    }
    dp1[0] = 0;
    dp2[0] = 0;

    d1tmp[0] = 1;
    for(int i = 0;i < n;i++){
        for(int j = 0;j < vec[i].size();j++){
            int l = i;
            int r = vec[i][j].first;
            int p = vec[i][j].second;

            if(d1tmp[l]){
                dp1[r] = max(dp1[r], dp1[l]+p-(r == n ? 0 : a));
            }else{
                dp1[r] = max(dp1[r], dp1[l]+p-(r == n ? a : a*2));
            }

            dp2[r] = max(dp2[r], dp2[l]+p-(r == n ? a : a*2));
            dp1[r] = max(dp2[r], dp1[r]);

            d1tmp[r] = 1;
        }
        dp2[i+1] = max(dp2[i], dp2[i+1]);
    }

    int ans = 0;

    for(int i = 0;i <= n;i++){
        ans = max(ans, max(dp1[i], dp2[i]));
    }

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