void* calc(void* arg)
{
    long* x = data.a;
    long mysum = 0;
    long i, lock;
    long start, end;



    pthread_mutex_lock(&mutex2);

    start = x[*(int*)arg * LENGTH];
    end = start + LENGTH;

    pthread_mutex_unlock(&mutex2);


    for (i = start;i<end;i++){
        mysum += x[i];
    }

    pthread_mutex_lock(&mutex);
    data.sum += mysum;
    pthread_mutex_unlock(&mutex);

    pthread_exit((void*) 0);
}