#include<cstdio>

#include<algorithm>

#include<iostream>

#include<cstring>

#include<vector>

#include<stack>

#include<cmath>

#include<queue>

#include<map>

using namespace std;

const int maxn=;

int sum[maxn<<],b[maxn<<];

void pushup(int rt)

{

    sum[rt]=sum[rt*]+sum[rt*+];

    b[rt]=min(b[rt*],b[rt*+]);

}

void change(int rt,int l,int r,int x,int y,int c)

{

    int m=(l+r)>>;

    if(l==r)

    {

        sum[rt]=b[rt]=c;

        return;

    }

    if(x<=m&&b[rt*]<c)change(rt*,l,m,x,y,c);

    if(y>m&&b[rt*+]<c)change(rt*+,m+,r,x,y,c);

    pushup(rt);

}

int main()

{

    int n,m;

    while(~scanf("%d%d",&n,&m))

    {

        int x,y,z;

        memset(sum,,sizeof(sum));

        memset(b,,sizeof(b));

        for(int i=; i<m; i++)

        {

            scanf("%d%d%d",&x,&y,&z);

            change(,,n,x+,y,z);

        }

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

    }

    return ;

}