#include<iostream>
#include <cmath>
using namespace std;
int main()
{
    double b=1.0/3.0;
    double s=0;
    cout << "e="; 
    double e;cin >> e;
    int n=1;
    while (fabs(b)>= e)
    {
        s += b;
        b=-b/9.0;
        n++;
    }
    cout << "s=" << s << endl;
    system("pause");
    return 0;
}