#include <stdio.h>
#include <string>
#include <cstring>
#include <stdlib.h>
#include <math.h>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <list>
#include <iterator>
#include <assert.h>
#pragma warning(disable:4996) 

typedef long long ll;
#define MIN(a, b) ((a)>(b)? (b): (a))
#define MAX(a, b) ((a)<(b)? (b): (a))
#define LINF 9223300000000000000
#define INF 2140000000
const long long MOD = 1000000007;
using namespace std;


int main(int argc, char* argv[])
{
    int n,m,a;
    scanf("%d%d%d", &n, &m, &a);

    vector<vector<pair<int,int> > > v(n+1);
    int i;
    for(i=0; i<m; i++) {
        int l,r,p;
        scanf("%d%d%d", &l, &r, &p); l--;
        v[r].push_back(make_pair(l, p));
    }

    vector<ll> dp(n+1);
    vector<ll> sdp(n+1);
    dp[0]=0;
    for(i=1; i<=n; i++) {
        dp[i]=sdp[i-1]-(i==n? 0: a);
        int k;
        for(k=0; k<(int)v[i].size(); k++) {
            dp[i]=MAX(dp[i],dp[v[i][k].first]+v[i][k].second-(i==n? 0: a));
        }
        sdp[i]=MAX(sdp[i-1],dp[i]);
    }
    printf("%lld\n", sdp[n]);

    return 0;
}