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

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N, M;
    long long A;
    cin >> N >> M >> A;
    vector<int> Ls(M, 0);
    vector<int> Rs(M, 0);
    vector<long long> Ps(M, 0LL);
    vector<int> idx(N + 1, -1);
    vector<int> next(M, -1);
    for (int i = 0; i < M; ++i) cin >> Ls[i] >> Rs[i] >> Ps[i];
    for (int i = 0; i < M; ++i){
        int r = Rs[i];
        next[i] = idx[r];
        idx[r] = i;
    }
    vector<long long> dp(N + 1, 0);
    long long record = 0;
    for (int i = 1; i <= N; ++i){
        dp[i] = record - A;
        int pos = idx[i];
        while (pos != -1){
            int L = Ls[pos];
            long long score = dp[L - 1] + Ps[pos] - ((i == N) ? 0 : A);
            dp[i] = max(dp[i], score);
            pos = next[pos];
        }
        if (dp[i] > record) record = dp[i];
    }
    cout << record << endl;
    return 0;
}