#include<cstdio>

 #include<cstring>

 #include<iostream>

 #include<algorithm>

 #define IOS ios::sync_with_stdio(false);//不可再使用scanf printf

 #define Max(a, b) (a) > (b) ? (a) : (b)

 #define Min(a, b) (a) < (b) ? (a) : (b)

 #define Mem(a) memset(a, 0, sizeof(a))

 #define Dis(x, y, x1, y1) ((x - x1) * (x - x1) + (y - y1) * (y - y1))

 #pragma comment(linker, "/STACK:102400000,102400000")//栈外挂

 using namespace std;

 inline int read()

 {

     int x=,f=;char ch=getchar();

     while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}

     while (ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}

     return x*f;

 }

 typedef long long ll;

 const int maxn =  + ;

 const int MOD = ;//const引用更快，宏定义也更快

 #define MID(l, r) ((l) + ((r) - (l)) / 2)

 #define lson(o) ((o)<<1)

 #define rson(o) ((o)<<1|1)

 struct node

 {

     int l, r, lazy, sum;

 }tree[maxn * ];

 void pushup(int o)

 {

     tree[o].sum = tree[lson(o)].sum + tree[rson(o)].sum;

 }

 void pushdown(int o)

 {

     if(tree[o].lazy > )

     {

         int lc = lson(o), rc = rson(o);

         tree[lc].lazy = Max(tree[lc].lazy, tree[o].lazy);

         tree[rc].lazy = Max(tree[rc].lazy, tree[o].lazy);

     }

 }

 void build(int o, int l, int r)

 {

     tree[o].l = l;

     tree[o].r = r;

     if(l == r)

     {

         tree[o].lazy = tree[o].sum = ;

         return;

     }

     int m = MID(l, r);

     build(lson(o), l, m);

     build(rson(o), m + , r);

     pushup(o);

 }

 int ql, qr;

 int v;

 void update(int o)//懒惰标记

 {

     //cout<<o<<" "<<tree[o].l<<" "<<tree[o].r<<" "<<ql<<" "<<qr<<endl;

     if(ql <= tree[o].l && qr >= tree[o].r)tree[o].lazy = Max(tree[o].lazy, v);

     else

     {

         int m = MID(tree[o].l, tree[o].r);

         if(ql <= m)update(lson(o));

         if(qr > m)update(rson(o));

     }

 }

 void query(int o)

 {

     if(tree[o].l == tree[o].r)//如果是叶子节点，那就计算sum值

     {

         tree[o].sum = Max(tree[o].sum, tree[o].lazy);

         return;

     }

     pushdown(o);//不是叶子节点，那就把懒惰标记传递下去

     query(lson(o));

     query(rson(o));

     pushup(o);//计算总和。

 }

 int main()

 {

     int n, m;

     while(scanf("%d%d", &n, &m) != EOF)

     {

         Mem(tree);

         build(, , n);

         while(m--)

         {

             ql = read(), qr = read(), v = read();

             ql++;

             update();

         }

         query();

         printf("%d\n", tree[].sum);

     }

     return ;

 }