#include <iostream>
#include <iomanip>
#include <limits>
#include <math.h>
 
int main(){
	double PI = 0;
	double Delta = std::numeric_limits<double>::epsilon() * 2;
	double k = 0;
 
	while (Delta > std::numeric_limits<double>::epsilon()){
		Delta = (4 / (8 * k + 1) - 1 / (4 * k + 2) - 1 / (8 * k + 5) - 1 / (8 * k + 6)) / pow(16.0 ,k);
		PI += Delta;
		k++;
	}
 
	std::cout << std::setprecision(16) << "PI => " << PI << " k => " << k << std::endl;
 
	return 0;
 
}

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