#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>

long ans = 0;
pthread_mutex_t lock;

void* calc(void* args) {
    int sec = *(int*)args;
    int p_ans = 0;
    for(int i = sec * 250000; i < (sec + 1) * 250000; i++) {
        p_ans += i;
    }
    pthread_mutex_lock(&lock);
    ans += p_ans;
    pthread_mutex_unlock(&lock);
    return NULL;
}

int main() {
    pthread_t thread[4];
    pthread_mutex_init(&lock, NULL); 
    int arr[4] = {0, 1, 2, 3};
    for (int i = 0; i < 4; i++) {
        pthread_create(&thread[i], NULL, calc, &arr[i]);
    }
    for (int i = 0; i < 4; i++) {
        pthread_join(thread[i], NULL);
    }
    printf("Final answer: %d\n", ans);
    pthread_mutex_destroy(&lock); 
    return 0;
}