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

void chmax(int64_t& a, int64_t b){
    a = max(a, b);
}

int main(){
    int N, M, A;
    cin >> N >> M >> A;
    vector<pair<int, int>> R2LP[100001];
    for(int i=0; i<M; i++){
        int l, r, p;
        cin >> l >> r >> p;
        R2LP[r].push_back({l, p});
    }

    const int64_t INF = 1e18;
    vector<int64_t> dp(N+1, -INF);
    dp[0] = 0;
    int64_t mx = 0;
    for(int i=1; i<=N; i++){
        for(auto& p : R2LP[i]){
            int l = p.first, pt = p.second;
            int64_t cost = (i == N ? 0 : A);
            chmax(dp[i], dp[l-1] - cost + pt);
        }
        chmax(dp[i], mx - A);
        chmax(mx, dp[i]);
    }

    int64_t ans = *max_element(dp.begin(), dp.end());
    cout << ans << endl;
    return 0;
}