#include <iostream>
#include <vector>
#include <cassert>
using namespace std;
typedef long long ll;
typedef pair<int,ll> P;
int N,M;
ll A,dp[100010] = {};
vector<vector<P>> v(100010);

int main(){
    cin >> N >> M >> A;
    assert(N<=100000 && M<=100000);
    int l,r;
    ll p;
    for(int i=0;i<M;i++){
        cin >> l >> r >> p;
        assert(l<=r);
        v[r].push_back(P(l,p));
    }
    ll ma = 0;
    for(int i=1;i<=N;i++){
        dp[i] = ma-A;
        for(auto x:v[i]){
            dp[i] = max(dp[i],dp[x.first-1]+x.second-(i==N? 0:A));
        }
        ma = max(ma,dp[i]);
    }
    cout << ma << endl;
}