#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<ll,ll> ;
const int INF = 1e9;
const int MOD = 1000000007;

int main(){
    ll n,m,a;
    cin >> n >> m >> a;
    vector<vector<P>> section(n+1);
    rep(i,m){
        ll l,r,p;
        cin >> l >> r >> p;
        --l;--r;
        section[r+1].push_back(P(l,p));
    }

    vector<ll> dp(n+1);
    ll ans = 0;
    dp[0] = 0;
    for(int i=1;i<=n;i++){
        if(i==n){
            dp[i] = ans;
            for(P s:section[i]){
                dp[i] = max(dp[i],dp[s.first] + s.second);
            }
            ans = max(ans,dp[i]);
            continue;
        }
        dp[i] = ans - a;
        for(P s:section[i]){
            dp[i] = max(dp[i],dp[s.first] + s.second - a);
        }
        ans = max(ans,dp[i]);
        //cout << dp[i] << endl;
    }
    cout << ans << endl;
    return 0;
}