#include<cstdio>
#include<algorithm>
#define COGS
using namespace std;
const int maxn=1000010,maxm=1010,INF=100000000;
struct t{
	int l,r,num;
}pro[maxm];
int n,m,r,f[maxn];
inline bool cmp(const t &a,const t &b){
	return a.r<b.r;
}
inline void in(){
	#ifdef COGS
	freopen("milkprod.in","r",stdin);
	freopen("milkprod.out","w",stdout);
	#endif
	scanf("%d%d%d",&n,&m,&r);
	for (int i=1;i<=m;i++){
		scanf("%d%d%d",&pro[i].l,&pro[i].r,&pro[i].num);
	}
}
inline void deal(){
	sort(pro+1,pro+m+1,cmp);
	pro[0].r=-INF;
	for (int i=1;i<=m;i++){
		for (int j=0;j<i;j++){
			if (pro[j].r+r<=pro[i].l)
			  f[i]=max(f[i-1],f[j]+pro[i].num);
		}
	}
}
inline void p(){
	printf("%d",f[m]);
}
int Main(){
	in();
	deal();
	p();
	return 0;
}
int main(){;}
int xlm=Main();