// Evaluate Pi Using Leibnitz Formula

/* =============================================== *
 *                 LEIBNIZ FORMULA                 *
 *                                                 *
 *            1       1       1       1            *
 *  pi = 4 [ --- (-) --- (+) --- (-) --- (+) ... ] *
 *            1       3       5       7            *
 * =============================================== */


#include<iostream>
using namespace std;

int main()
{
    double pi;
    int n = 100000; // number of terms to consider

    for(int i = 1; i <= n; i++)
    {
        int denominator = (2 * i - 1);
        // (2i-1) is formula of odd number

        if ( i % 2 == 1)
        {
            pi += 4.0 / denominator;
        }
        else
        {
            pi -= 4.0 / denominator;
        }
    }

    cout << pi << endl;

    return 0;
}