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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n, m, A, l, r, c;
    cin >> n >> m >> A;
    vector<vector<pair<int, int>>> g(n);
    for(int i = 0; i < m; i++){
        cin >> l >> r >> c;
        l--, r--;
        g[l].emplace_back(r, c);
    }
    const ll INF = 1ll << 60;
    vector<array<ll, 3>> dp(n, array<ll, 3>({-INF, -INF, -INF}));
    dp[0][0] = dp[0][1] = dp[0][2] = 0;
    for(int i = 0; i < n; i++){
        for(auto &&pa : g[i]){
            tie(r, c) = pa;
            dp[r][2] = max(dp[r][2], dp[i][1] + c);
        }
        dp[i + 1][0] = max(dp[i + 1][0], dp[i][0]);
        dp[i + 1][1] = max(dp[i + 1][1], dp[i][0] - A);
        dp[i + 1][0] = max(dp[i + 1][0], dp[i][2] - A);
        dp[i + 1][1] = max(dp[i + 1][1], dp[i][2] - A);
    }
    cout << *max_element(dp[n - 1].begin(), dp[n - 1].end()) << '\n';
}