#include <iostream>
#include <vector>

#define ll long long

using namespace std;

int main()
{
    ll int cant, q, maximo = 0, s = 0;

    cin >> cant >> q;

    vector <ll int> DP(cant + 2);

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

        cin >> d >> h >> k;

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

    for(auto i:DP)
        s += i, maximo = max(maximo, s);

    cout << maximo << endl;

    return 0;
}