from collections import defaultdict

sums = defaultdict(int)
_, n_ranges = (int(x) for x in input().split())

for _ in range(n_ranges):
    start, stop, value = (int(x) for x in input().split())
    sums[start] += value
    sums[stop+1] -= value

max_val = running_val = 0
for _, val in sorted(sums.items()):
    running_val += val
    max_val = max(max_val, running_val)

print(max_val)