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

 
signed main(){
    //cout << setprecision(12) ;
    ios::sync_with_stdio(false);
	cin.tie(0);

    ll n,m,a;
    cin>>n>>m>>a;
    vector<vector<pair<ll,ll>>> v(111111);
    for(ll i=0;i<m;i++){
        ll l,r,c;
        cin>>l>>r>>c;
        l--;
        v[r].push_back(make_pair(l,c));
    }
    vector<ll> dp(n+1,-a);
    dp[0]=0,dp[n]=0;
    ll ans=-1e18;
    
    for(ll i=1;i<=n;i++){
        ll ret=0;
        for(auto j:v[i]){
            ret = max(ret,dp[j.first]+j.second);
        }
        dp[i] = max(dp[i]+ret,ans-a);
        ans = max(ans,dp[i]);
        
    }
    ans = max(ans,0LL);
    cout<<ans<<endl;


    
}