#include <iostream>
#include <cstdlib>

using namespace std;

int factorial(int n)
{
    if (n<=1)
    {
        return 1;
    }
    else
    {
        return n*factorial(n-1);
    }
}

int main()
{
    setlocale(0, "rus");
    double e;
    cout << "Введите e: ";
    cin >> e;
    double sum = 0;
    double temp;
    int i = 1;
    while ( (temp = 1.0/factorial(2*i)) >= e )
    {
        sum += temp;
        i++;
    }
    cout << sum << endl;
    system("PAUSE");
    return 0;
}