#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <array>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
#include <memory>
#include <regex>
using namespace std;

class Data
{
public:
    int l, r;
    long long p;
    bool operator<(const Data& other) const{
        return l < other.l;
    }
};

const long long INF = LLONG_MAX / 2;

int main()
{
    int n, m;
    long long a;
    cin >> n >> m >> a;
    vector<Data> v(m);
    for(int i=0; i<m; ++i){
        cin >> v[i].l >> v[i].r >> v[i].p;
        -- v[i].l;
    }
    sort(v.begin(), v.end());

    vector<long long> dp(n+1, -INF);
    dp[0] = 0;
    int k = 0;
    long long tmp = 0;
    for(int i=0; i<m; ++i){
        while(k <= v[i].l){
            dp[k] = max(dp[k], tmp - a);
            tmp = max(tmp, dp[k]);
            ++ k;
        }
        dp[v[i].r] = max(dp[v[i].r], dp[v[i].l] + v[i].p - a);
    }

    long long ans = *max_element(dp.begin(), dp.end());
    ans = max(ans, dp[n] + a);
    cout << ans << endl;

    return 0;
}