#include <iostream>
#include <cstring>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <set>
#include <utility>
#include <cstdlib>
#include <queue>
#include <stack>
#include <iomanip>
#include <cstdio>
#include <map>
#include <list>

using namespace std;

typedef long long Int;
typedef pair<Int,Int> P;

#define rep(i,x) for(Int i = 0; i < (Int)(x); i++)
#define rrep(i,x) for(Int i = ((Int)(x) - 1); i >= 0; i--)
#define _upgrade ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define all(x) (x).begin(), (x).end()
#define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() );
#define pb push_back
#define MX 100010


template<class T1, class T2> void chmin(T1 &a, T2 b){if(a>b)a=b;}
template<class T1, class T2> void chmax(T1 &a, T2 b){if(a<b)a=b;}

//ll gcd(ll a, ll b){return b?gcd(b,a%b):a;}
//ll lcm(ll x, ll y) {return x / gcd(x, y) * y;}

Int dx[4] = {1,0,-1,0};
Int dy[4] = {0,1,0,-1};
const Int INF = 1001002003004005006ll;
const Int mod = 1e9 + 7;
const double PI = 3.14159265358979323846;


// ****************************************CODE***************************************//






int main()
{
        int n,m,a;
        cin >> n >> m >> a;
        vector<map<int,Int>> ma(n+1);
        for(int i = 0; i < m; i++)
        {
                int l,r,p;
                cin >> l >> r >> p;
                ma[r][l] += p;
        }

        vector<Int> dp(n+2, -1e17);
        dp[0] = 0;
        Int tmp_maxi = 0;
        for(int i = 1; i < n+1; i++)
        {
                int cost = a;
                if(i == n) cost = 0;
                for(auto pa : ma[i])
                {
                        chmax(dp[i], dp[pa.first-1] + pa.second- cost);
                }
                chmax(dp[i], tmp_maxi-a);
                chmax(tmp_maxi, dp[i]);
        }
        cout << *max_element(all(dp)) << endl;
        return 0;
}