#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>

#define N 1000

sem_t lock;
int shared = 0;

void *inc(void *arg) { (void)arg;
    for (int i = 0; i < N; i++) {
        sem_wait(&lock);
        shared++;
        sem_post(&lock);
    }
    return NULL;
}

int main(void) {
    pthread_t t[2];
    sem_init(&lock, 0, 1);
    for (int i = 0; i < 2; i++) {
        pthread_create(&t[i], NULL, inc, NULL);
    }
    for (int i = 0; i < 2; i++) {
        pthread_join(t[i], NULL);
    }
    printf("%d\n", shared);
    sem_destroy(&lock);
    return 0;
}