#include <stdio.h>
#include <time.h>
#include <math.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/times.h>
clock_t u_clock()
 { struct tms t;
   return times(&t); }
int main()
{ clock_t t1, t2;
  long long int i, n=10000000000;
  double pi=0.0, x, use;
  t1 = u_clock();
#pragma omp parallel for private(i,x) reduction(+:pi)
  for (i=1; i<=n; i++)
    { x  = i;
      pi = pi + 6.0/(x*x); }
  t2 = u_clock();
  use = (double)(t2 - t1)/100.0;
  pi = sqrt(pi);
  printf("n=%ld, pi=%f\n",n,pi);
  printf(" use time=%f  sec\n",use);
  return 0; }