#include <iostream>
#include <iomanip>
using namespace std;
#include <math.h>
void Seriessummation(int n, int j)
{
    int i, k;
    double ans = 0.0, m, pi, P;
    pi = acos(-1);
    for (i = 1, k = 1; k <= n; i += j)
    {
        m = 4.0 / i;
        if (k % 2 == 1)
            ans = ans + m;
        else
            ans = ans - m;
        k++;
    }
    if (n <= 100)
        cout << setw(12) << setprecision(11) << ans << endl;
    else
    {
        P = (pi - ans) / pi * 100;
        cout << setw(12) << setprecision(11) << ans;
        if (n == 50000)
            cout << setiosflags(ios::fixed) << setprecision(6) << "        " << P << "%" << endl;
        else
            cout << setiosflags(ios::fixed) << setprecision(6) << "       " << P << "%" << endl;
    }
}
int main()
{
    cout << "     纯手工原创打造" << endl;
    int n, j;
    double ans;
    cout << "NO.1: " << endl
         << endl;
    n = 12;
    j = 2;
    Seriessummation(12, 2);
    cout << "________________________________________" << endl;
    cout << endl;
    cout << "NO.2: " << endl;
    for (n = 50000; n <= 1000000; n = n + 50000)
        Seriessummation(n, j);
    return 0;
}