#!/bin/python3

import sys

if __name__ == "__main__":
    n, m = input().strip().split(' ')
    n, m = [int(n), int(m)]
    v = []
    for i in range(n):
        v.append(0)
    for a0 in range(m):
        a, b, k = input().strip().split(' ')
        a, b, k = [int(a), int(b), int(k)]
        for i in range(a-1, b):
            v[i] += k

print(max(v))