#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <omp.h>

// silly version ...
long sum_silly (int N){
  long sum = 0;
#pragma omp parallel for schedule(static,1) 
  for (int i = 1; i <= N ; i++) {
    sum += i;
  }  
  return sum;  
}

// less silly version ...
long sum_less_silly (int N){
  long sum = 0;
#pragma omp parallel for schedule(static,1)  
  for (int i = 1; i <= N ; i++) {
  #pragma omp critical 
    sum += i;
  }  
  return sum;  
}

// not silly version ...
long sum_not_silly (int N){
  long sum = 0;
#pragma omp parallel for reduction(+:sum) schedule(static,1)  
  for (int i = 1; i <= N ; i++) {
    sum += i;
  }  
  return sum;  
}

// not silly version (hand made) ...
long sum_not_silly_hand_made (int N){
  long sum = 0;
#pragma omp parallel
{
  long local_sum = 0;
  int start = N* omp_get_thread_num()/omp_get_num_threads() + 1;
  int end =   N*(omp_get_thread_num()+1)/omp_get_num_threads() + 1;
  for (int i = start; i < end ; i++) {
    local_sum += i;
  }  
#pragma omp critical
  sum += local_sum;
}
 return sum;  
}

int main (int argc, char *argv[]){
  long N = atoi(argv[1]);
  printf("exact = %ld\n",(N*(N+1))/2);
  printf("silly = %ld\n",sum_silly(N));
  printf("less silly = %ld\n",sum_less_silly(N));
  printf("not silly = %ld\n",sum_not_silly(N));
  printf("not silly hand made = %ld\n",sum_not_silly_hand_made(N));
  return 0;
}