#include <iostream>
#include <conio.h>
#include <math.h>
#include <chrono>
#include <ctime>

using namespace std;

int main()
{
    int i;
    int j=0;
    int N=1;
    double x;
    double z;
    double err;

    auto start = std::chrono::system_clock::now();
    do
    {
        x=0;

        for(i=1; i<=N; i++)    // wartosc PI
            {
                z=pow((i-0.5)/N,2);
                x =x+ 1/(1+z);
            }
            x=4*x/N;

            //cout<<x<<endl;

        err = x-M_PI;
        N=N+10;

    }while(err>=1.5e-6);

     do
    {
        x=0;

        for(i=1; i<=N; i++)    // PI value
            {
                z=pow((i-0.5)/N,2);
                x =x+ 1/(1+z);
            }
            x=4*x/N;

            //cout<<x<<endl;

        err = x-M_PI;
        N++;

    }while(err>=1e-6);
    auto end = std::chrono::system_clock::now();

    std::chrono::duration<double> elapsed_seconds = end-start;
    std::time_t end_time = std::chrono::system_clock::to_time_t(end);

    cout<<"Nmin is = "<<N-1<<endl<<"Error for Nmin is = "<<err<<endl<<endl;

    std::cout << "finished computation at " << std::ctime(&end_time)
              << "elapsed time: " << elapsed_seconds.count() << "s\n";

    return 0;
}