#include <stdio.h>
#include "mpi.h"
#include <math.h>

const long long int n = 1000000000;

double f( double x )
{
    return (4.0 / (1.0 + x * x));
}

const double start = 0.0;
const double end = 1.0;

const double PI25DT = 3.141592653589793238462643;

int main(int argc, char *argv[])
{
	int id, np;
	MPI_Init(&argc, &argv);
	MPI_Comm_rank(MPI_COMM_WORLD, &id);
	MPI_Comm_size(MPI_COMM_WORLD, &np);

	double a = ( end - start ) / n;
	double P = 0;

	for ( int i = id; i < n / 2; i += np )
	{
		double b = 4 * f( start + (2*(i+1)-1) * a ) + 2 * f( start + (2*(i+1)) * a );

		P += b;
	}

	if(id == 0) 
	{
		double zbir=P;
		for( int i = 1; i < np; i++) 
		{
			MPI_Recv(&P, 1, MPI_DOUBLE, i, 20, MPI_COMM_WORLD, NULL);
			zbir+=P;
		}
		double myPi = ( zbir + f( start ) - f( end - a ) ) / 3.0 / n;
		printf("%.16lf\n", myPi );
		printf("Error is %.16f\n", fabs(myPi - PI25DT));
	} 
	else  
		MPI_Send(&P, 1, MPI_DOUBLE, 0, 20, MPI_COMM_WORLD);

	
	MPI_Finalize(); 
	return 0;
}