def main():
    first_input = input().strip('\n').split(' ')
    N, M = [int(x) for x in first_input]

    target_list = [0] * N

    max_v = 0
    # Loop through the input range
    for i in range(0, M):
        input_line = input().strip('\n').split(' ')
        a, b, k = [int(x) for x in input_line]
        # Modify list
        for j in range(a - 1, b):
            target_list[j] += k
            if target_list[j] > max_v:
                max_v = target_list[j]

    print(max_v)


if __name__ == '__main__':
    main()