#include <cstdlib>
#include <cstdio>
#include <algorithm>
using namespace std;
const int MAXN=30100;
class Tree
{
public:
	int s,e,t;
}T[5100];
int N,H,ans=0;
int hash[MAXN];

bool cmp(const Tree&a,const Tree&b)
{
	if(a.e!=b.e) return a.e<b.e;
	return a.s>b.s;
}

inline void init()
{
	scanf("%d\n%d\n",&N,&H);
	for(int i=1;i<=H;i++)
		scanf("%d%d%d",&T[i].s,&T[i].e,&T[i].t);
	sort(T+1,T+1+H,cmp);
}

inline void greedy()
{
	int have,next;	
	for(int i=2;i<=H;i++)
	{
		have=0;
		for(int j=T[i].s;j<=T[i].e;j++)
			if(hash[j]) have++;
		if(have>=T[i].t) continue;
		next=T[i].t-have;
		for(int j=T[i].e;j>=T[i].s;j--)
		{
			if(hash[j]) continue;
			hash[j]=1; ans++;
			next--; if(!next) break;
		}
	}
}

int main()
{
	freopen("trees.in","r",stdin);
	freopen("trees.out","w",stdout);
	init();
	for(int i=T[1].e;i>=T[1].s;i--)
	{
		ans++; hash[i]=1;
		if(ans==T[1].t) break;
	}
	greedy();
	printf("%d\n",ans);
	return 0;
}