#include <stdio.h>

#define N 2000000000

#define vl 1024

int main(void) {

  double pi = 0.0f;
  long long i;

  #pragma acc parallel vector_length(vl) 
  #pragma acc loop reduction(+:pi)
  for (i=0; i<N; i++) {
    double t= (double)((i+0.5)/N);
    pi +=4.0/(1.0+t*t);
  }

  printf("pi=%11.10f\n",pi/N);

  return 0;

}