#include <iostream>
#include <vector>

#define ll long long

using namespace std;

int main()
{
    ll int cant, act, maximo = 0, t = 0;

    cin >> cant >> act;

    vector <ll int> n(cant + 1);

    for(ll int i = 0; i < act; i++){
        ll int d, h, k;

        cin >> d >> h >> k;

        n[d] += k;
        n[h + 1] -= k;
    }

    for(ll int i = 1; i <= cant; i++)
        t += n[i], maximo = max(maximo, t);

    cout << maximo << endl;

    return 0;
}